This also happens in CC4 and CC5.
During a Stalingrad GC the game would crash at the end of the last battle of the turn in single player, every time. Upon going back to reload it, the save file was gone.
I was able to hex edit the save file. I removed both BGs out of the save file in order to advance to next round. This was a short term fix and I was hex editing blindy. Only by trial and error I found the BGs. Having to remove the BGs was worst case scenario, it was just a back up plan. Long term effects are unknown.
When my opponent and I played that battle, it went fine, no crash and the file saved on both computers. I don't know why it worked here. I did not have to resort to hex editing the save file.
I saved the file when it was giving me crashes, and two weeks later when I play it, no crashes. So its got me stumped as why this happens.
Theres a few things you can do on your own to "fix" this to continue the GC. You need to have back up save files to do these.
1. In the forcepool selection screen, replace all your troops, do this for opponent as well.
2. Upload the file to someone else and see if they can truce through the battle.
3. Switch sides by hex editing save file and attempt to truce through battle. http://www.closecombatseries.net/CCS/modules.php?name=Content&pa=showpage&pid=119
4. Play that battle online.
5. Reinstall the game in a different folder.
Basically with these options your trying to change any variables within the game that may be causing the crash.
Nothing I have found can bring these saved games back. They are in memory though and no data is truly deleted off the HD until its written over. What you can do is find an undelete program and it may be able to restore the save file. Good freebie versions of this kind of software is hard to find, good luck!