That would depend on the government to notice and take action. I imagine if one person left and the company put a suitable replacement in, it may not be noticed and wouldn't likely draw any lawsuit. But swapping in a "D team" as described would likely provoke a response.

When I was doing contractor jobs, in one of the projects personnel rotation was met with a hefty penalty. So the PMs tried their best to keep us happy, which meant a lot of the guys took advantage to ask for a generous raise. This was BTW a pretty non significant and easy support operations support project, so I imagine this terms were standard for other projects.

In those cases the customer has to approve the replacement (within reason). Comes with a price premium though.

My first job out of college was a practically fly-by-night video game development house that had primarily D-team members except for a couple of contractors and me.

After my first successful project for them, their biggest client started demanding that I be assigned to their next big project (or one of the external contractors). We both ended up taking jobs elsewhere, and that client quit using the developer.

And the client? They were a full-on shovel-ware developer that barely cared about game quality. They just needed a game that would run reliably enough that Nintendo would approve it. So to be fired as a developer by that company was really embarrassing...

Here is one such "key personnel" clause: https://www.law.cornell.edu/cfr/text/48/2052.215-70