The company would have to remove all contributions of external developers though. If the project was not licensed under the GPL, but external contributors did contribute to the project under the GPL, then it seems to me that either the company has to release the project under the GPL, or remove all the third-party contributions and any code that might be derived from those contributions (since it would be a derived work). Realistically they would have to revert the project to where it was before the first external contributor contributed and rewrite all subsequent development from scratch.
This makes me think, you could have a friend develop a MVP which you use as a starting point for your project. For example, if you want to create a game, I could write a simple event loop and render a couple triangles on the screen, then give this to you as an example, and with an agreement that you can build upon it.
Thus, everything you do will be a derivative work of what I started. If your company tries to take it, I can come in and cause problems for them.
That is basically what caused the minecraft craftbukkit server drama. Their distribution contains modified priority code from mojang. And contributions are in GPL. Some contributor decides to use GPL to claim server source code (while obviously they can't). And there is obviously no way to fix the situation. Ends up as the craftbukkit server repo dead forever.
