Is an early escape normal in encounter 1C?
Yes, this is a normal situation.  It isn't very fun, sure, but it is a normal one.  I've had it happen several times and each time I swear off playing this scenario until I find a new group of victi-- friends who have not yet experienced my wra-- version of fun.

In fact, I had a situation where one of my players simply wanted to "try and leave to see what happens".  Everyone else followed.  Game over in the first couple of turns.