There's an entire industry called "source code escrow" for this problem. If someone is concerned that you'll go out of business, you can escrow your stuff, and

There's an entire industry called "source code escrow" for this problem. If someone is concerned that you'll go out of business, you can escrow your stuff, and they can continue to run it and modify it. You can probably create a proper license so they can use it internally however they want but not sell it/give it away.