I think, if aeris came back in the ending it would be something like this:
avalancha is in the higwind. Suddenly, aeris appears...i think barret, cid, tifa, vincent and the others would approach her, and very happy they would say:
- aeris, you are back!!
but cloud, would not approach. He would rest shocked, happy but at the same time...he would not know what to say...so aeris would approach him...and thenshe would smile.
-Cloud...its a pleasure to meet..the real you
Yes. She would be with the " real" cloud and i think he would not know exactly what to say, now that he knows aeris was zack girlfriend.
-Aeris...you are..back
-yes, cloud...
and then, he would express his joy. But he would not say;
aeris, oh, i love you!.
i think after this, they would continue to see each other and one day, cloud would confess his love....or mayibe is aeris who would do firts....what do you think?