I know i would do a low dose to keep it away.Some people have reintroduced bryopsis into their tanks or didn't run the treatment long enough(or the right dosage) to kill all of the roots and it came back in a few tanks.There's been several that I know of that had so much in their tanks that they ran more than one treatment to get rid of it all as well. If you kill all of the bryopsis,it won't return without you bringing it back into your tank. From all of the research that I/others have found there is no such thing as spontaneous generation of bryopsis without it coming from a bryopsis cell.
GHA can come back once the conditions are right for it's regrowth. It's pretty much a part of our hobby but we're still experimenting on some low dose continuous use of fluconazole to combat this and things are looking pretty good.