If a doctor removes too much fat with upper bleph...will that fat grow again? What happens to the eye with age... skin droops?

It would be very helpful to see some before and after pictures to answer this question.  There is fat in the lids that extends back behind the eye.  With age, some of this fat may move forward.  So after your fat removal, you may notice some fullness again after several years.  In the meantime, you can fill under the bone with some hyaluronic acid filler, or fat.  If you have some excess skin that can be excised.  It may make the lid appear deeper however.   

During an upper eyelid blepharoplasty if too much fat is removed the fat does not grow back. The future result as one ages cannot be predicted.

Quite difficult to respond without photos.  You could undergo additional skin resection which is a minor procedure.  The results would be definitive whereas fat grafting does have a degree of uncertainty.  Everyone ages differently and prognostication as to your personal situation would require a consultation.