Seroma after explant and capsulectomies. It is possible that this will resolve or do I need to insist he take another look?

Small seromas may resolve. Let your plastic surgeon know and see if a small drain can be placed in the office. 

In my experience with over 1000 explantations, the following is very important in order to avoid problems.  Total capsulectomy, use of drains for 5 to 7 days, compression with a breast binder from surgery until two weeks postop, and use of nonreactive dissolvable sutures (not braided).  You will not only need drainage, but also removal of the entire capsule again as some have most likely reformed.  This is often a very difficult operation, so I recommend that you go to surgeon who specialize in explantations.  If complications of cosmetic surgery are not excluded from your insurance, we can usually get insurance coverage for the explant and probably for the seroma surgery as well.  Take a look on the internet at the information I have written on problems with breast implants.