Extrait du guide:
if your campaign crashes, simply edit the campaign.ini file in the crashed campaign folder within the Missions/campaign/NA concerned folder, and copy the last mission’s reference under the crashed one, like this:
[Main]
ExecGenerator DGen.exe
Class il2.game.campaign.CampaignBlue
awardsClass il2.game.campaign.AwardsDEfighter
- 10622.mis
10706.mis
10706.mis
end.mis
In that case there was a mission generated on July 6th, 1941, which crashed, and by copying it again as shown in red above, one may restart flying the campaign.
This last trick may work if your campaign data files are not bugged, but you had a crash due to a hardware failure for instance.