I have a nonfiction book out which isn't selling well at all. :( And yet, it's gotten rave reviews from every industry professional who's read it. I'm looking ahead to when it's discontinued and the rights revert to me. Is it possible that another publisher might want to buy it, despite its poor sales track record? What if I substantially rewrite and reformat it? Thank you!
Not likely unless something new has occurred to make your topic hot.
Your best bet is to republish it yourself by true self-publishing, not through some vanity press that claims to be a self-publisher.
If you do all the promoting (and writing!) then you should make all the profit. Publishers do not push books unless they expect big sales. The selling part is all up to you.