For me, it's not just that they screwed up the API changes, it's that they've repeatedly kept doubling down since then.
It's also ... I keep thinking back to Ellen Pao. They brought her in knowing that they wanted her to get rid of FPH and Victoria, knowing that at least the FPH thing was going to make her a target of the misogynistic GamerGate haters and bringing in a woman anyway, and they deliberately and repeatedly refused to give her any public support. It was completely reprehensible, and they cheerfully scapegoated her and kicked her to the curb when it was done.
As bad as that was, I also see elements of the same thing happening here, where this is a highly unpopular change, and there's no one else from reddit speaking up to support spez. I think they're going to have him force through the changes and then kick him to the curb like they did Ellen. They're not going to reverse any of the changes - it's what they want, after all, but they're going to let spez take all the heat and go on their merry way completely unphased.
To be completely honest, I think spez deserves this: his job as CEO is to have vision, manage public relations, and handle crises, and he's miserably failed at all of those. He misunderstood reddit's most valuable assets (it's commentary and the large group of people contributing and moderating the site for free), and he literally paid the API fees for some very profitable and potentially profitable companies to suck every piece of data from reddit; then he publicly targeted small publishers who enhance reddit instead of presenting them as collateral damage of the AI wars (I suspect to avoid bringing attention to his incredible lack of vision in letting everyone freely harvest data for their own lucrative products). And he's clearly failing in the PR and managing crises front as well. But I truly believe that everyone at reddit is perfectly happy to let spez do this thing that they want done, and then they'll throw him away when it's done in an attempt to appease the users.
Anyway, your question is "what will I do if reddit undoes the API changes". Given my beliefs, I simply don't see how I could possibly trust reddit management ever again. And trust is a really big thing with me; I don't think I could ever go back.
Unless you're reddit management, here to gauge user temperament, in which case I will totally return if the API changes are undone, yes, of course I will, just trust me!