The crushing damage is 2d8+8 and another 8pts of acid damage. So if you figure average rolls we'll have 25pts of damage per round from being inside. That would equal a DC 22 + spell level or 28 for word of recall. 12th level Cleric has +16 in Concentration with 12 con, but I think before battle he'll cast a maximized endurance for 15 con. So he'll have +17 concentration, which isn't consistently good enough to beat a DC28 even IF he prepares word of recall. He knows they're in trouble so he might not.... They also have a magic item called a refuge stick that when broken takes them back to the guys room who helped them, I have a feeling he'll use this.