There's been a lot of long-time speculation on what kind of body Al will end up in (assuming he does at all; the anime doesn't seem to be concerning itself with that particularly any more). Some theorize that he'll get his own 10-year-old (or 15-year old, since time seems to pass beyond the gate) body back again; others think he might end up in a homunculus body, or Rose's baby.
But as it turns out, we've already got a perfectly good body floating around without a soul. Why shouldn't Al end up in Nina's body? I'm sure Tucker could be 'persuaded' to lend it to the purpose. And considering the way people keep turning up again unexpectedly in this series, who knows whether they could show up at the last minute. It certainly would wrap up a few loose ends nicely. To say nothing of how weirdly it would screw up interpersonal relationships in the show
This week's installment of Wacked-Out-Theories has been brought to you by origami_box.