Gamma ray bursts are produced by stars that are very massive and short-lived. So one can argue that after few tens of millions of years a cluster wouldn't produ

Gamma ray bursts are produced by stars that are very massive and short-lived. So one can argue that after few tens of millions of years a cluster wouldn't produce that them. On the other hand you are of course right - in a galaxy that is still undergoing intense star formation it is still dangerous to live in a dense region where a nearby young cluster can still render your home planet sterile through a GRB. However, our own Galaxy doesn't seem to be forming stars that actively anymore, and the chance of a new GRB pointing directly at a given star cluster is negligible.