I have a question regarding file locks when opening DWG files.

Say user A connect to a server X using VPN and via the network open a file which is located on file server Y and saves it from time to time. User B then cannot open that file as it is locked by user A. What I would like to know for certain is what happens if the VPN connection for user A temporaily drops, is the file lock then lost at the server so that user B can open and edit the file and potentially overwriting the changes user A has made, or potentially causing them to work on the same file at the same time? What about file locks and their timeout period in this scenario?

/Andreas