I do not have a solution for the problem, as I do not have much experience in Alice either..

However, as a tip, if something like this happens, go to the folder where you saved your world, and you will most likely find a folder which says <world name> backups. If you open it, you can find backups of your world that Alice automatically saved, thus allowing you to return to a slightly previous version that might still work properly. Then you wouldn't have to start from scratch anymore..