Parting ways with an agent while on sub -

If the hypothetical person is sure they're ready to leave Unhelpful Agent, they have a couple of choices: after reading their agency contract to follow the correct termination procedure,

-They can ask the agent in their termination letter to contact the houses to pull the submission.
-They can terminate the relationship and email the houses to let them know to contact them directly and not the agent. But if the submission should sell to one of those houses, the agent will receive his or her commission and be agent of record for the sale.

No matter what path the hypothetical person chooses, he or she should request a complete submission history and not rest until it's received. These are broad suggestions--there may be circumstances that modify what course is chosen.

And when Hypothetical Person begins to query other agents with the new novel, save discussion of the former novel/agent for when a new agent offers rep. There's no need to bring it up earlier.

Best wishes to the Hypothetical Person.

No, I don't think so. The author's relationship (or lack thereof) with a former agent doesn't really matter: if they love the book and think it will sell well and make them money, they're gonna acquire it. If they don't, they won't.

When you end your relationship with an agent they will usually pull all submissions that they've made on your behalf--unless one is close to an offer or a contract. The author shouldn't contact those publishers. It's the agent's job.

I do think you should put your dilemma in the "Second Circle of Hell" thread. There are folk there who have been in tricky agent relationships that they've managed to work out with the agent. There are others who have split from agents and found new ones. Bear in mind, once a book has been submitted by one agent, other agents will consider it shopped, and likely won't take it on.

My feeling is that you'd have to write something new to submit to other agents.