I have tried fixing your file, by using the new feature “collapse” that will be released in Alpha 8. It works, but unfortunately the file I save is not backwards compatible with your version (Alpha 7).
I see only 2 solutions for you right now…
1) You try to free up some memory, so you can load your file. Then you can fix the most data consuming drawings (those towards the end is worse) by tracing them one by one on to a new blank drawing and then deleting the old ones (no lassoing!). This will clear it all up and give you a small file size when you save, so you can load it anytime.
2) You wait for Alpha 8, and use the new collapse feature. It will probably be released in a few weeks if all goes well.
I hope this helps you after all.