Mac OS X 10.8 crashes after Thunderbolt display disconnect and sleep
Solution 1:
Did you look in ~/Library/Logs/CrashReporter/ if there are new entries that date from the crash? Or look at the syslog (Utilities, Log-Viewer) if anything shows there prior to the hang?
Solution 2:
As described in my update, I ran sudo pmset -a hibernatemode 3 to reset the sleep mode and I've had only two of those crashes in the last six months.
FWIW, running two Thunderbolt displays on a lid-closed MacBook is hell. Now that I only use one Thunderbolt display, things are generally much more reliable.