As far as I'm aware there has never been a mail to warn players of a guild town's deletion and none of the games code suggests this was ever the case either.
However, maybe the confusion comes from the fact that the message that printed to World Chat when a guild town has been deleted reads as the following:
"Guild GUILD_NAME's Town is about to be confiscated due to insufficient membership. Anyone interested in taking over, please find the guild administrator to apply."
This message has always read this way since aslong as I have played so I can see where confusion comes from.
I'm also sure that the 3 person rule is working as when we created the staff towns on the classic server me and Doudou where running our own tests on this to make sure it was working. Aslong as you login 3 unique characters after the maintenance has been completed your town should be fine as once this has been reached it will no longer check the guilds activity until next maintenance.