Will Belly Pouch Flatten out After Seroma?

it's hard to really tell what's going on from your description. In general once a seroma is adequately treated and no longer present the skin will heal as it normally would have if the seroma was not present. Any remaining puffiness is due to residual swelling that hasn't yet resloved, or some left over fat. 

Seromas occasionally correct abdominoplasty is properly treated with serial aspiration it should have no effect on the appearance of the abdominoplasty. Inadequately treated seromas can lead to a chronic problem that can leave a lump in might require a second operation.

It is possible that your seroma has completely resolved and you have some degree of soft tissue swelling which is not unusual after an abdominoplasty.  Continue to follow up with your plastic surgeon and at the 4 -6 months you may need to be re-evaluated possibly for some touch up liposuction. 

Your plastic surgeon will be your best resource when it comes to precise advice and/or reassurance. Generally, it takes many months for swelling to resolve after tummy tuck surgery and/or  drainage of seroma and it may take up to one year  (or greater)  a complete skin redraping  to occur.

I hope this helps.