The dangers of queenless hives

We have been having a bit of correspondence with someone whose two hives have both become queenless. We have copied in a beekeeper friend, Mark, whose expertise is well in advance of ours. The discussion is important to us as we too have found that one of our eight hives has become queenless. We are planning to merge this hive with another. Mark has advised that it needs to be done as soon as possible. A queenless colony can see some worker bees start laying. These bees are infertile but when a fertile queen is added to the colony, the infertile fake queens can end up killing the new one. Clearly this is something we want to avoid. We don't want rogue bees killing the queen of the hive to which they have been added. It means we will have to do the hive merger in the next couple of days.