After hours of work, saving frequently, I get a "too many heaps sections" error and crash. Now my file refuses to load. GIMP says unable to parse XML. Is there a way to recover a file in Inkscape?

Since the XML can't be parsed, there's no way to fix it in Inkscape. You will have to fix it by hand. If you can't work out how to fix it yourself, post a copy somewhere so that we can have a look at it.