The problem with the theory that the dwarves would all ally with Durin's Bane in order to reclaim Moria for themselves is that dwarves are notorious for holding grudges and the balrog won't be exempt from this, six thousand years later or no. I could see dwarves waiting for the balrog to march with his army and then come in from behind to retake their ancestral home by force, but not an alliance. If anything, the dwarves or a subset of them might be more willing to join Sauron's invasion force in exchange for the promise of being vanguard troops in Moria. They won't trust Sauron, but that doesn't mean they'd think they could get rooted out of Moria a second time, not when Sauron's forces would be depending on the dwarves to guide them.
