There's an issue on KeeperFX Resource Tracker that could be fixed by changing level script:
https://code.google.com/p/keeperfx/issues/detail?id=44
My idea is to add a LOSE_LEVEL condition with a proper message if the player won't claim the portal fast enough to get a dragon.
What do you think of it? Who will do it?
DL, this seem like a perfect occasion for your first commit to KeeperFX repository .