There’s a problem with saving!

Most likely, you’ll have to start everything from scratch. You should have saved the campaign.sav file. It contains information about completed missions and hero upgrades. You can ask someone to send you theirs. Just not me, because I’m playing the campaigns in version 3.0. But in that case, the heroes will be upgraded according to the preferences of the person who sends the file. Ideally, the game versions should match. I’m not sure if a campaign.sav file from versions 1.5-1.6 will work due to differences in the skill wheel. Mine definitely won’t work – it will immediately require a mod that allows you to play all campaigns in version 3.0. And I haven’t even reached the 4th campaign yet.