Brother's excoworker closed corporate Dropbox account, all files gone on machine

It sounds very unfortunate and a difficult lesson to learn, but there's 2 key takeaways. Never mix your personal and work things, second always have backups or a redundant place information is stored especially if it's irreplaceable.

My understanding is that linking personal and business accounts in Dropbox doesn't give the company any access to your personal account. Therefore if the business one was cancelled it should not effect the personal one. It sounds like he wasn't switching between personal and work diligently when storing personal files.

Now the touchy area. If the ex-employee cancelled the account maliciously there maybe some legal recourse. This would very much depend on the communication. Because his side maybe that he was contacted after termination and told to cancel it because it wasn't work sanctioned.