I have several ideas involving Tifa in Midgar in a variety of scenarios, both with and without her father, but they're all vague and sometimes self-contradicting or in slightly differing verses, so I'm not sure.
I don't know what she'd do in Midgar either, but I have the mental image of her and Cloud sharing a very small apartment and paying bills together and being all underage-coupleish, and also the mental image of Tifa becoming some sort of idol singer - either before or after she met him - and all the guys lusting after her while Cloud was all "...I dare not reveal our connection to these crazed fanboys..." and such XD; My head is a mish-mash of AU concepts that never come to life (vide my journal).