Is there a future Buddha?

In the Pali Tipitaka I think it's mentioned (only) in the Buddhavaṃsa:

In the twenty-eighth section is given the names of three Buddhas, namely, Taźhałkara, Medhałkara and Saraźałkara who lived before Dřpałkara Buddha at different intervals of the same world cycle. The names of other Buddhas (up to Gotama Buddha) are also enumerated together with the name of the kappas in which they have appeared. Finally there is the prophesy by the Buddha that Metteyya Buddha would arise after him in this world.

There are sutta references to previous Buddhas, so ...

And I believe it's a more prominent feature of other Buddhist schools (and texts) -- see Maitreya.

Good householder,

It's mentioned, in an urgency by displaying causes of samvega, that a further Buddha will arise, yet exactly this Sutta DN26 urges to train for liberation in this life, while the mentioned fake monks and teacher, lead people to get into this terrible times...

The body of this sutta consists of a narrative illustrating the power of skillful action.

In the past, unskillful behavior was unknown among the human race. As a result, people lived for an immensely long time — 80,000 years — endowed with great beauty, wealth, pleasure, and strength. Over the course of time, though, they began behaving in various unskillful ways. This caused the human life span gradually to shorten, to the point where it now stands at 100 years, with human beauty, wealth, pleasure, and strength decreasing proportionately. In the future, as morality continues to degenerate, human life will continue to shorten to the point were the normal life span is 10 years, with people reaching sexual maturity at five. "Among those human beings, the ten courses of action (see AN 10.176) will have entirely disappeared... The word 'skillful' will not exist, so from where will there be anyone who does what is skillful? Those who lack the honorable qualities of motherhood, fatherhood, contemplative-hood, & brahman-hood will be the ones who receive homage... Fierce hatred will arise, fierce malevolence, fierce rage, & murderous thoughts: mother for child, child for mother, father for child, child for father, brother for sister, sister for brother." Ultimately, conditions will deteriorate to the point of a "sword-interval," in which swords appear in the hands of all human beings, and they hunt one another like game. A few people, however, will take shelter in the wilderness to escape the carnage, and when the slaughter is over, they will come out of hiding and resolve to take up a life of skillful and virtuous action again. With the recovery of virtue, the human life span will gradually increase again until it reaches 80,000 years, with people attaining sexual maturity at 500. Only three diseases will be known at that time: desire, lack of food, and old age. Another Buddha — Metteyya (Maitreya) — will gain Awakening, his monastic Sangha numbering in the thousands. The greatest king of the time, Sankha, will go forth into homelessness and attain arahantship under Metteyya's guidance.

The story, after chronicling the ups and downs of human wealth, life span, etc., concludes with the following lesson on kamma and skillful action.

Buddha is a word to describe certain qualities of a human person. Of course such one carries his last body in this very life.

The honorific 'Buddha' means 'awakened one'. Since the intent of Buddhist philosophy and practice is to lead people to awakening, then there must ipso facto be future Buddhas, or else the entire project is fruitless.

If you take 'Buddha' to refer specifically a teacher of the (pure, unadulterated) dharma, then you're thinking about Maitreya. As this wikipedia article points out, the idea that a new teacher will arise after the dharma has been forgotten appears in some of the later sutras; see the sources section. The Maitreya has undeniably been expanded and exaggerated in the traditions of certain Buddhist sects, but that's as may be...

The arising of a new Buddha does not imply the reincarnation of the earlier Buddha. It merely means that some world-bound being has cast off the cloak of selfhood and realized the true nature of things. There's nothing mystical or mysterious in that. If the architect building our house leaves, another architect will come along to finish the job; the new architect does all the same things that the old architect did, but that doesn't make the latter a reincarnation of the former.