User81,
I’m sorry to hear about your problem with the deleted blocks. It looks like we have a bug where some blocks are deleted unnecessarily when components are deleted . The correct behavior is supposed to be that only the blocks that reference the deleted components are removed. It also seems like there is a problem with the undo behavior in the Blocks Editor. We will definitely look into these issues.
I’m so glad that you were able to rebuild your app!
As for backup, right now the best way to do that is to share the project with yourself. The share operation will make a snapshot copy of your project at that point in time and when you go to the resulting URL it will create a copy of that snapshot in your set of projects. I hope that help you.
-Mark