1200 calories is recommended daily intake for every human being so you should stick to this diet program. Maybe it seems to you it so to little but it is quite enough. Avoid junk food which is high in calories but can satisfy your hunger for a short period of time.
The fat around your stomach shouldn’t be back if your surgery was performed by the book. Complications after tummy tuck are rare.
About your second question I think it would be best to consult with your doctor because he is familiar with your situation better than anyone else so there is no need to guess what could happen.
Anyway I hope that everything is going to be just fine. And if you have problems to maintain 1200 calories per day increase your water intake. This will help you to feel full longer.