What happens to the debt?

I wonder what happens...

With all this employee termination and shutting down of government agencies and such, I have to wonder what happens when they shut down a government agency that holds federal debt.

Is the debt returned to Treasury? This would mean the gross federal debt is reduced by that amount.

Or is the debt grabbed by Musk or somebody? This would mean that payments against that debt go to the grabber. That would be a real incentive to shut things down.

It would be nice to know.