Apocalypse should be stranded in the temporal purgatory because he can't rejuvenate anymore because according to TOS the X-Men destroyed his rejuvenation chambers thus he's unable to exist outside of said realm.
Spoiler!
I admittedly had to look this up because I barely remembered what you were talking about, let alone the shitty 5th season. But apparently in the 5th season Apocalypse came back by inhabiting the body of Fabian Cortez.