Data recovery / backup should have been step #1.... this was a machine that was hit by lightning. Attempting to boot the machine with anything that was inside it when it got hit is a risky proposition. If the drive wasn't already dead, it could easily be killed.
Sounds like things are in a "good enough" state, but honestly the real issue seems to be that this customer doesn't have a proper backup system in place. That's where I'd go next. This quickbooks file is key for not only payroll, but also filing their taxes at the end of the year and probably even more. They need a system in place so that even if the building burns down, they can be up and running the next day without risk of losing everything.
Seems like that quickbooks file is in "public" documents so it can be network shared, using that machine as the "host".