These server mergers are clearly too much for the available dev team to handle and they cause far too much disruption to the rest of the servers playtime. In the future if a particular server has to be shut down, give the people who are on it a chance to migrate to a server of their choice free of charge. That mechanism is already in game, you don't have to merge anything. There is no reason to do these merging events if they cause so much trouble.
Not sure what a big deal it is even if it ends up bring 48 hours of downtime. Not like there will be several servers mergers in the next year. We don't have enough servers do it that many times