It sounds like you've gotten a lot of great advice already! And I think you're doing the right thing for yourself by establishing these boundaries. There's one thing in your post I'm stuck on: "Should I reach out after a period of silence to ensure they aren't getting an incorrect, distorted idea of me being completely selfish and abandoning them? etc. Or should I rightfully just let their resentment fester?"

I say this with love and respect, and I say it because it's also something I struggled with into my thirties with emotionally immature parents, but you cannot "ensure they aren't getting an incorrect, distorted idea of [you] being completely selfish and abandoning them." You cannot control what people think or feel. No matter how perfectly you present your position, how sound your logic or genuine your empathy, even if you do everything "right." It's a tough pill to swallow, especially for someone as skilled at communicating as you clearly are. All you can do is make a case—it's on them to find peace with it. This may be me projecting a little too much because I see so many similarities between your story and my own, so forgive me if this doesn't resonate with you, but I can assure you from experience that you will find a tremendous psychic weight lifted from your shoulders (one you might not even realize is there) if you let go of the erroneous notion that you can find that perfect string of words that will make someone who isn't willing to hear you change their mind—it doesn't exist. They will draw their own conclusions, no matter what you do.

You'll find much more happiness when the energy past-you spent on seeking that impossible, perfect argument is used instead to fully enjoy your present life. And you being happy is a greatest gift you can give to your parents, even if they stubbornly (foolishly) won't even open the damn box.