No, you can't save it manually, it is automatically saved every 10 seconds (something like that) and also when quitting the game, but we can introduce a command to also force-save it manually. But I'm afraid that won't help with your problem, because something seems to go wrong with the saving procedure itself.
So your worlds are still available, but everything you changed in the world will be reverted the next time? Are you using steam or standalone version? Tried to start the application as administrator?
//Edit: Okay just saw your post in the other thread that you are using the standalone. In which folder did you extract the game from the zip? There seems to be something wrong wit accessing the files, since you are saying in the other thread that corrupted worlds can't be deleted (never seen this issue before). Perhaps running the application as administrator (rightclick on the exe) may solve your problem.