I'm guessing that crappy ISP is the one that wants to disconnect from my network.

If you are leaking routes you shouldn’t then a decent ISP will disconnect your crappy network.

It happens a lot, usually because of mistakes, it’s typically fixed quickly.

Feel free to null route or redirect any IP you want in your network. Just don’t be surprised when other networks cut you off if you advertise those routes out of your network, and don’t be surprised when your customers are unhappy because you aren’t transporting the packet to the target IP as is your job.

If you really believe what you’re saying, which I find hard to believe myself, I recommend you try doing what you’re saying and report back the results.