It is down to what a station can handle, there isn't a firm rule on this. At some places they can't keep a lounge open late because staff have children, pets, elderly relatives to get back to. At other times, if it is known in advance that the departure is going to be delayed then staff may well be agreeable to flex their rotas around, indeed may prefer it to their original rota. I do know SFO has stayed open for at least some recent A380 late running. So there is some attempt to do this, it doesn't always work.