@Sturgis,
The problem is, he's going to have to disappear, bam, and not be seen again, or have any sort of communication.
Your last suggestion is what I was thinking about suicide.
Either suddenly gaining a conscience and not being able to live with himself, or simply seeing it as a viable next step.
They could just replace Frank, like they did in Betwitched. All of a sudden, one morning, there was a new Darren. I don't know, maybe Spacey has the rights to his character.
Any of these solutions seem rather lame though, considering how HOC was ususally able to pull off something you didn't see coming.
Honestly, I feel bad for the people who acted or otherwise worked on the show who were suddenly out of a good job.