Do you have references to best practice, or examples where you have recovered Models or can you share your expertise on how to avoid the "Unable to save model" error within ModelBuilder using ArcGIS 10.1 for Desktop?
Alternatively can you advise on situations to avoid which cause this error to occur.
There is very little help information on this topic.
There is a linked question here Do you use a proven workflow to edit and document ArcGIS ModelBuilder models? - that shares advice on how to track the building of models, so you always have a clean copy of the model to go back to. Comment there if you have comments about the process of tracking edits / changes to Models.