Community

STARTING THE ADVENTURE
Is that white sandy area like a sinkhole from the surface - where part of the tavern the PCs were getting drunk in fell into the hole? - I know The Jakes out the back - where they are going to the loo - falls down a deep well leaving them hanging.

REALWORLD SUBSIDENCE
Well...dont know the scale But if the squares represent 5' feet the big rooms (50 feet across) must have greater than fifty feet of stone ceiling thickness above them or the ceilings will be at 100% subsidence. i suppose the 'rocks' in those large rooms could represent some failure of the overlying strata putting the big rooms down as places where if anything happens to give them a shake - like a fireball spell the mountain will fall in on them. You would need insitue stone columns occupying large areas of the big caves to stop the ceiling from falling in - block collapse would mean large square sections would fall in - not necessarily the whole chamber at once.
Disintergration to cut a tunnel will infact stress the strata causing the strata to collapse - the ceiling of the new tunnel will fall in (the crawl toward subsidence increases with the speed of excavation - instantaneous disintergration results in instantaneous failure).

A WORTHY FOE
The PCs encounter the BBEG - a DWEORG (Historically: A Dweorg is an ancestor to Dwarves) in this case Dwei- means Dire so the PCs are facing a Dire Dwarf (Stat that bugger up from templates - he should be 8 feet tall with a taste for human flesh but highly intelligent - probably armed with an electric cattle prod). His plan (along with any other Dweorg present) might be to carve out the big caves and collapse them underneath important buildings in the community - so the Guild treasure vault and the locked store house filled with food and stuff will fall into the big caves.