The answer is Yes and No

Yes - The sources exist
No - It's really no use anyway.

Even as backups of source code repositories exist, it still means it is fairly difficult to do anything useful, and fairly doubtful if any new development can be easily started.
The whole SW production machinery (building, testing, qc, packaging, signing,...) would have to be implemented really from scratch, without people who have done it before. It would be a fairly large task indeed.