Unfortunately, we have a big bug to deal with: of my four savegames, two of them are corrupt and unloadable. IIRC both of them are on 50x50 maps (one on basemod's Valley map, one either on Valley map or a shrunken version of basemod's Cradle map), which may be related to the problem; after all, they're the same maps which had graphical issues if optimized tile drawing was off.
I recommend allowing multiple saves for a game. Sure, losing three years of gameplay may suck, but permanently losing a save is worse.