I had gastric bypass 5 years ago. I lost 100lbs, but have gained 50 lbs back. Might I be a candidate for revision surgery?

Eating behavior KEY. Tips for eating success: don't drink fluids with meals (washes food down); avoid high fat snacks (chips, crackers, peanut butter); avoid sugar, eat more solid food that "packs your pouch", avoid too many slider foods that go right through. Can also see your surgeon for endoscopy or solid meal UGI to check size of pouch and pouch outflow size.
Yes, but. You need to work out the reasons that you have gained back so much weight. It is not likely due to a failure of the surgery but rather becoming too liberal with diet restrictions.