Well first off, know that you’re not alone! In fact there’s another thread here on CC from someone else who just got the same news.
Best bet would be to start with Vassar’s CDS. Check the admissions stats in section C especially. They do break out ED applicants/accepted, so from there you can then back into an RD acceptance rate. Since you’re now in the regular pool, at the end of the day that’s the place to start to assess your chances.
From there, take a look at the various test and GPA data they report in the CDS. You should be able to find how your stats compare to their enrolled kids.
I’m 100% positive that the answer to your specific question, “Has anyone ever gotten deferred and gotten in?” is Yes. For sure.
Good luck to you from here on out!