How likely is hematoma to come back after being treated?

If you had the appropriate surgery for a hematoma and your surgeon was satisfied that there was no more bleeding.  You should be fine. Too much strenuous activity can reinstitute the bleeding. Please follow your surgeon's instructions carefully as well as keep you follow appointments.

Hello Gnaz8,
It sounds like the hematoma was appropriately reexplored operatively and the bleeding stopped.  In this setting it would be very unusual to recur.  If you have signs or symptoms similar to your previous episode, you should contact your plastic surgeon right away.  But otherwise, you should be good to go.  Good luck!
Dr. William Albright
ABPS board certified plastic surgeon

It would be useful to know the type of
surgery and location of the hematoma. If
not evacuated small hematomas last about three months. Some can become chronic and need surgical
removal. If it was evacuated surgically
and the bleeding controlled, it would rarely come back later. Some fluid collections could be lymph rather
than blood and could be more complicated, again, it depends on the location to
determine this.