Who revoked their signatures from the union agreement at the Council of Florence?

The primary delegations at Florence were led by the Pope and the Emperor. In essence, both of them led their respective delegations in the original signing—though a prominent Greek, Mark Eugenikos never signed—while the Russian delegations were coerced by Isidorius.

The Greek delegation's acceptance of the union was declared invalid a few years later by an assembly of prelates in Constantinople. This was an uniform collective action on behalf of the entire Eastern Church due to religious imperatives; the Russians withdrew to form their own church due to political imperatives. Minor Eastern churches continued to follow their unions and I've indicated specific signatories below.

Signatories

It is difficult to find a specific list, but I found two accounts which detail the majority of the important members who signed, one with a focus on the East and another with its focus on the Russian churches. I apologize for the long quotations, but I don't find much use in rewriting this as a list.

_{The day was fixed, when the signing of the decree should take place. Dorotheus of Mitylene proposed to the Pope beforehand, to bribe over some of those who had not as yet consented to the union, and bribes were in fact resorted to. On the 5th of July the whole Council of the Easterns assembled in the Emperor’s palace. The Emperor was the first to sign the decree. The Metropolitan of Heraclea was absent on account of his illness, but was even obliged to sign the decree in his bed. No one thought of disturbing Mark of Ephesus, being convinced of his firmness. Isidore, Bessarion, and the Protosyncellus, joyfully signed their names. Then followed the signatures of the Metropolitans of Monemvasia, Cyzicum, Trebizond, Nicomedia, Tornovo, Mitylene, Moldovlachia, Amasia, Rhodes, Drystra, Gana, Melenicus, Drama, Anchialus, and those of eleven persons from the lower grades of the Constantinopolitan clergy. The Greeks signed without reading the decree beforehand. Its contents were only known to those who had drawn it up. At all events, most of the Greek Bishops conceding to the Pope’s wish, and the Emperor’s will, gave a written, though reluctant, consent to the unjust union. Even those who were not allowed to vote at the Council, were now made to sign. Exceptions were only made for those who had either died, as the Patriarch Joseph, and the Metropolitan of Sardis, or those who had managed to get away from Florence, as was done by Isaiah of Stauropol and the Bishop of Tver.}

_{When all the Greek Bishops, in the presence of the Cardinals, had affixed their signatures to the Council decree, then the Emperor sent ten of the eldest Bishops to witness the signing of the decree by the Pope. Eugenius, after carefully examining the signatures of the Greek Bishops, asked while himself signed the decree, whether the Ephesian had signed? He was told that he had not. “Then nothing have we done,” involuntarily exclaimed the Pope. Eight Cardinals signed their names after the Pope, about sixty Bishops, and a good many Abbots.}

^{—Ostroumov, 'The History of the Council of Florence'}

_{The fact that one of them is the Ethiopian bishop, whose church signed the Decree of Union...}

_{He [Isidor] had led the Muscovite delegation to the Council, and had signed the Union proclamation and forced the other Russian delegates to also sign, not out of political motives but because of his deep study of the issues.}

_{In agreement with the Byzantines, Isidor signed the Decree of Union for the whole metropolis of Kiev, including Moscow. Abraham of Susdal and others who had come from Moscow with him refused to do so. Isidor was made a Cardinal by Pope Eugene and appointed legate to facilitate the application of the Union.}

_{—Hamerman, 'The Council of Florence'}

I didn't find a specific person from the Armenian delegation who signed their respective union with Rome, as declared in the Decretum pro Armenis. This union was not revoked by the Armenians who signed, though there were many who didn't go along with this, creating a split in the Armenian church.

The Coptic representative was one Abbot Andrew, sent by Patriarch John of Cairo. The Ethiopian representatives was Peter, from an Ethiopian monastery in Jerusalem sent by its Abbot Nicodemus. Peter and Andrew signed their Union on February 4th, 1442, and this was proclaimed in the Cantate Domino.

This text, Dezhnyuk's 'The Council of Florence' disagrees with Hamerman about the Ethiopians in the status of their representative. Also, Dezhnyuk goes out of his way to emphasise that the Abyssinian church was not menitioned in the Cantante Domino, indicating that "this could be additional evidence that Peter did not have credentials to represent his church". The "bishop" who is mentioned by Hamerman I found no evidence of.

The Syrians were represented (already in Rome and not Florence) by Abdale, Archbishop of Edessa, and their union with Rome was declared in the Mulla et Admirabilia. The Chaldeans were represented by Timotheus, Archbishop of Tarsus, joining Rome on August 7th, 1445, and this was declared in the Benedictus sits Deus.

Revokings

The most important person on the Greek side had not signed—Mark Eugenikos or Mark of Ephesus—so he could not recant. His abstention also made him quite popular with the Greek populace due to the speeches the Greek prelates made on their return. Despite Mark refusing the patriarchal throne on their return to Constantinople, the new Patriarch Metrophanes died relatively soon after taking office, leaving the pro-Union Greeks in even greater disarray (as Metrophanes had made a written promise to honour the union).

Soon after, the remaining Orthodox prelates as led by Arsenius of Caesarea along with the patriarchs—Philotheus of Alexandria, Dorotheus of Antioch, and Joachim of Jerusalem—declared that all of the Greeks who conspired to preserve the union were acting contrary to Orthodox doctrine, and were as heretics deprived of their dignities and under threat of excommunication. These decisions, along with speeches by Mark of Ephesus, caused Georgius Scholarius to stray from his affirmation of the union. John Eugenicus, Syropulus, and Gemistes Pletho were the next to raise their voices against the union.

Though Ioannes VIII assigned his confessor Gregory Mamma the position of the Patrarch of Constantinople, his death shortly afterwards allowed Philotheus, Dorotheus, and Theophanes to assemble in the capital. The assembly of the Orthodox prelates deprived Mamma of his position, and jointly, with the new Patriarch Athanasius, refuted the union for the whole of the Eastern Church. This action represented the symbolic withdrawal of the entirety of the Orthodox party's consent to the union.

The Russian churches rejected the union in 1448 to Muscovy's political imperatives by defining their Russian Orthodox Church as autocephalous. The religious basis for this was the rejection of the Filioque contrary to what had been agreed at Florence.

Further Reading

My sources primarily have been Ostroumov's and Hamerman's accounts as described above while Dezhnyuk was instrumental in supplying information on the minor church delegations.

The main overviews of these events in English seem to have been written by Friar Joseph Gill. He has two books, 'The Council of Florence' and 'Personalities at the Council of Florence', both of which might interest you.