If I stopped hormones just after a couple months, and got gyno surgery, would  that completely prevent me from having breasts if I decided that hrt in the future is the best path for me?

Probably. It depends on whether they remove the actual glandular tissue that is necessary for growth, but most gynecomastia surgeons will try to do that (since most cis men don't want a recurrence). If you simply get fat removed to make them look flatter, that might not affect later development, although there are never any guarantees.

If you have been on hormones for a while, stopping them cold turkey could cause problems.

Part of whether your chest looks flat by removing fat depends in part on whether or not you were small to begin with. Lifting weights, especially bench presses could make your chest look more muscular and less like a female

Sam 1234