Siddharta steps back 10 feet (am allowed a single move of max 30 ft, right?), hope Bruce is not in the way, but then again, Bruce can fly at will, no?...)
and cast another disintegrate, on the 'thing'. dc 25.
then move upward on any stairs he finds with Bruce in the lead..
OOC: The plans never mentioned any cellars. Trying woudn't nescisarily hurt, but depending on the strength of the floor, you may or may not join the thing one level down covered in rubble.