>>Without addressing your question, the real answer is for the backup process to notify users that have files open 2 minutes or so before it kills their connections - or, failing that, send a broadcast message to all w/s that may be running and logged in. That lets interactive users shut down gracefully; non-interactive or unattended processes will still get killed ungracefully - but that's no different from what's happening now.
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>The problem is, no one is addressing my question. Everyone has advice on how to change the backup process, which I don't own. I need to know about the possibility of data corruption when the plug is pulled on an open file that is idle.

Everyone's workstation and network environment is different. If you really want an accurate idea, you could test by opening some (scratch) table(s) and then deliberately disconnect your network cable. Do this a few times and you should have a pretty good idea.

I still think killing connections without a warning to interactive users is unacceptable. If the "owners" can't, or won't mend their ways, you could create a reminder .EXE in VFP on your local HD and schedule it to run every evening at 11:55 pm. If you're not there and your machine's not running, nothing happens.