I just recently ran into the issue of a corrupt Lair database due to an improper shutdown. The cause, indicated by the error, was a corrupted WiredTiger.wt file. The fix for this is to submit a JIRA ticket to the guys over at mongodb (https://jira.mongodb.org/) explaining your issue, a copy of the stack trace, and a copy of your WiredTiger.wt and WiredTiger.turtle files. They sent over the fixed versions of the files shortly after (1 hour).

This led to a successful repair and the recovery of all of my lair data!