In the Eastern Orthodox tradition, is it possible to laicize a bishop?

It appears that for autocephalous Orthodox Churches, their Holy Synod has the authority to laicize them.

Although the person in question was "demoted" to monk and not fully laicized, I believe I have found an illustrative and extremely recent example (Wikipedia, which I quote below [editing out the references]; news source). The person in question, Monk Seraphim (Storheim), was convicted of sexually assaulting a young boy.

Following his release from prison, members of the Holy Synod of Bishops of the Orthodox Church in America on October 19–23, 2015 canonically deposed the retired Archbishop Seraphim from the status and all sacred functions of the episcopacy, removed him from the ranks of the clergy, and returned him to the status of a lay monk.

The Holy Synod made this decision with much sorrow, but with the conviction that it was a necessary action both for the salvation of the now Monk Seraphim and for the preservation of the good order and stability of the flock of Christ. At the same time, we offer our prayers for the victims, their families and all those who have been affected by the events surrounding this case.

Edited to add: With respect to your second question, I found this article on Professor Contantine Scouteris at the University of Athens on Christian Priesthood and Ecclesial Unity: Some Theological and Canonical Considerations. I have edited out the references again, but the original website has them. It appears that there is some debate on the matter, but at least some thinkers (such as Scouteris, with canonical basis) reject the idea of an indelible mark.

[...]the priest does not possess in himself an indelible mark as if it were a magical seal which grant him a private efficacy to perform the Eucharist or any other liturgical action, apart from the ecclesial body. The priestly ministry is rather a charismatic gift to serve and edify the body of the Church. It is a permanent rank of service only in union and by the discerning authority of the Church.

The doctrine of the "indelible mark" attained at ordination to the priesthood seems to have originated in the Scholastic period of the Western Church. This same conception was at times borrowed by Eastern theologians thereafter. [...] It is interesting to mention here that the sixth Ecumenical Council in its 33rd canon condemns the practice of Armenian Christians who had embraced the Old Testament custom concerning the Levitic rank and did not accept for the priesthood anyone who was not of this so called "priestly lineage". The reasoning for the adoption of the Old Testament typology in both cases seems to be that an identification mark is a constitutive element of priesthood. In the later case it is conceived as an inherited trait, while in the former which concerns us here, it is viewed as irrevocably and individually attained at the ordination rite.

The logical conclusion of the "indelible mark" is that the ordained individual possesses forever this peculiar mark of priesthood which can never be removed by anyone nor can it be surrendered in any circumstance. [...] Thus the ordained person possess a self sufficient power which is higher than the Church itself And the Church is not able to take back the indelible mark from an individual even if he is defrocked and excommunicated.

Interpreting the 68th Apostolic Cannon which refers to the impossibility of repeating the sacrament of ordination, St. Nicodimos the Agiorite explains that ordination cannot be repeated because it is done according to the Type of the First and Great Priest who entered once and for all into the holy of holies and there granted eternal salvation. Yet, he unswervingly rejects the doctrine of the "indelible mark" of priesthood and attests that it is the "invention of scholastics." Nevertheless, according to St. Nicodimos, the doctrine is borrowed by Nicholas Bulgaris, Koresios and many other theologians of the past century and some still somehow adhere to it today.