deram

Luckily Steam supported redownloading the 1.3.1. From KSP title context menu, select Properties -> Betas, and from optin dropdown menu select previous_1.3.1, and it starts downloading automatically. After short download, all progress in career there and all mods working. Thanks Steam, for making it possible, even if it was just the same Steam that auto-upgraded in first place. Hope this helps anyone else with same problems.