I've had it happen before where I've hit F1 on a server to save a cool map, then gone to another server and accidentally hit F1 instead of Esc while leaving, deleting the old saved map.
My suggestion is that, each time F1 is hit, it saves a new map, as lastsav.vxl, lastsav(2).vxl, etc...
Or take it a step further, and put a date/timestamp on it. I.E.
20110815-08:35:15.vxl
20120118-15:23:31.vxl
20120334-20:49:58.vxl
Any thoughts?