Ah-ah-ah... enspelled stone, remember? If the dungeon designer went to the trouble of warding it against physical attacks entirely, surely they'd give it considerable magic resistance as well (akin to the doors in the OC which are apparently warded against ALL spells, let alone "simple" ones.) In addition, "inferno"? I've never heard of this spell, clerical, arcane, psionic, or otherwise. Teleport would also be a solution - but not in Layonara, without DM help (and the dungeon designer could have incorporated teleport wards as well). *grins*
In addition, StF only allows the transformation of a 70 cubic ft. cylinder, and careful dungeon design could prevent that from being an escape in a mundane way (but really, if it's meant to be an effective trap, the walls would be warded against things like Passwall, let alone simple spells of this type.)
Regardless, as much as I applaud all this thinking outside the box, it was meant as a mental exercise, not as a test of the flexibility of ed. 3.5.