We’ve been having sporadic trouble with Indesign files that crash the application upon opening. It happens to a tiny percentage of files (99.9% are ok!). But when it happens it won’t work in any way.
We have tried broken documents on different macs and have tried ID2Q as well as Markzware themselves but they can’t fix the one we sent.
We keep previous versions of documents saved (in case a client changes their mind) and they are ok but something happens to a file that breaks it. It appears to only have been happening since CC and CC2014.
That is great that you are keeping previous versions. Documents can go kablooey, but as you said, fortunately it is very rare.
The best bet is just to figure out what might have been changed… for example, it could be a bad font, or a corrupt image that gets added to the file. Or it could be a glitch caused by working off a server. It’s probably impossible to track down without watching until it happens again.