I posted this exact scenario about three weeks ago on the NA server rules thread, as a "what-if". I wanted clarification because I knew this would happen. As soon as admins started kicking roof campers, not for being the last alive, but for being in inaccessible areas, the best tactic was to destroy their ladders. It was only a matter of time before someone was kicked for destroying the ladders.
http://forum.c-rpg.net/index.php/topic,776.msg48575.html#msg48575Unfortunately, no one clarified the issue.
The whole trolling excuse is just that, an excuse. People call each other friends, bundle of stickss, wishing them death by fire, etc on a daily basis, without getting kicked. I think if that's ok, telling someone they need to get down because their ladder is gone, is ok.
I also vote to get rid of ladders. If thats not possible, it should be a requirement that all mappers either make their roofs inaccessible or provide permanent access to them in some way.