I'm definitely considering top surgery, but am unsure about taking testosterone. If I don't take testosterone after periareolar top surgery, will the breast tissue come back? I know that with double incision there's no chance of breasts resurfacing, but I'm about a 30A and I don't think that my skin can stretch far enough for DI. Plus, I scar very easily (the scars I got back in 2007 are still prominent).
I really don't know. but since no one has answered this question, I will give my opinion.
I don't think the breast tissue will grow back if you are all the way through puberty. But if you gain weight after the surgery, fat might distribute to that area and make it look like you have breasts. Much in the same way a cis male would if he gained weight.
You might try asking your surgeon if you've already chosen one.
Though rare, under specific circumstances breast regrowth is possible even after DI (subcutaneous mastectomy). Percentage of remaining breast tissue varies by procedure and surgeon, but even with DI a common estimate is about 10% of the tissue remains.
A cis woman with a predisposition for massive breast tissue growth had a subcutaneous mastectomy, got pregnant, and had so much regrowth a second subcutaneous mastectomy was needed. The article makes it clear this is a rare event.
http://www.ncbi.nlm.nih.gov/pubmed/6240959
Obviously, someone small enough for peri doesn't have a predisposition for massive breast tissue growth, and many FTMs actively avoid pregnancy. If you're done with puberty, the surgeon does a good job removing most of the tissue, and you aren't exposed to high levels of feminizing hormones (such as in pregnancy) breast regrowth is not likely, but talk to your prospective surgeon(s) and review your options.
Relevant links you may find helpful:
http://www.ftmguide.org/chest.html
http://www.ftmguide.org/myths.html#5