If your project is OSS, what prevents them from taking it and "force you" (as an employee) to work on it anyway? Maybe a restrictive license may help: if your company takes the code and modify it, make them under the obligation of releasing the source code too. What is the current license of your project? Ultimately, nothing prevents you from deleting your public Git repo. You can decide that your project is not avai…
If they have even a debatable claim on the code (probably not but are you 100% sure?), then deleting it is destroying their property. That's a quick way to have a miserable life (getting fired, sued, blacklisted among peers, etc).
At least you are using the know how you gained during your work