Another Buddha -- Metteyya (Maitreya) -- will gain Awakening, his
monastic Sangha numbering in the thousands
Digha Nikaya 26 ref- http://www.basicbuddhism.org/index.cfm?GPID=29
I had to look up apocalypse, "the complete destruction of the world." That doesn't seem to be a theme in the Buddhist cosmologies where the universes have no beginnings and no ends.
(EDIT: Hmm, looks like I'm wrong-- the universe periodically falls to pieces and then rebuilds itself. But it isn't immanent-- a Mahakalpa is a long time from now, and a new universe rebuilds itself every time.)
Mappo, the time when the Dharma is forgotten and no longer taught is a Buddhist catastrophe, but more of a moral one.
Digha Nikaya 26 ag
Monks, a time will come when the children of these people will have a
life-span of ten years. And with them, girls will be marriageable at
the five years old. And with them, these flavours will disappear:
ghee, butter, sesame-oil, molasses and salt. Among them,
kudrusa-grain will be the chief food, just as rice and curry are
And with them, the ten courses of moral conduct will completely
disappear, and the ten courses of evil will prevail exceedingly: for
those of a ten-year life-span there will be no word for "moral", so
how can there be anyone who acts in a moral way?
Those people who have no respect for the mother and father, for
ascetics and Brahmins, for the head of the clan, will be the ones who
will enjoy honour and prestige.
Just as it is now the people who show respect for mother and father,
for ascetics and Brahmins, for the head of the clan, who are praised
and honoured, so it will be with those who do the opposite.
Mappo also leads to interesting consequences for current times, such as questions on if traditional forms of practice are effective anymore if we don't have a Buddha in the world. This is a big theme in Nichiren Buddhism.
When the Maitreya Buddha returns he is a like the historical Buddha, but in some accounts, much better. For people who care about the future Buddha, it is sort of like Pure Land Buddhism, where you wait to be reborn in a universe with an active, living, teaching Buddha. In Maitreya's case, that happens to be the same universe as our own. By the logic of Pure Land Buddhism, it seems like it would be more expedient to be reborn in the next life in the Amitabha's Pure Land.
Also interestingly, Maitreya played a big role in the White Lotus Rebellions, a political-religious movement in ancient China that lasted several hundred years that predicted Maitreya was returning right now. http://en.wikipedia.org/wiki/White_Lotus