AS long as there is a route available to them, they are not trapped. IF they had room to go off to the left, they could have scaled down the outside wall, especially if it was only one story tall. Yes, I know, they wouldn't actually scale the wall, but they could have moved off from the left edge where there was room, all of them running parallel to the board edge until they were able to move back to the table edge. Now, you would of course have to take the vertical movement into account for their descent to the bottom floor, but there is nowhere that I know of that says they have to moved down a level inside the ruin instead of outside it. So if there was a avenue to the left as was stated, they would have all run to the left on the level they were on as far as they needed to, then measured down to the bottom floor, and as long as they had their 1" between them and the two units on the bottom level, they would have been fine. If that could not have been done, then yes, they were trapped and destroyed.