Hmm yeah that's an interesting question. I know that for Pitt, those that are rejected pre-interview for MSTP are considered for MD admissions (e.g. interview) , but I'm not sure about post-interview MSTP rejections (or waitlists, for that matter). As you know, schools each have their own policies. For example, at Stanford, pre-interview MSTP rejections are sent to the MD-only office for consideration. During Stanford MSTP interviews, applicants are interviewed by both the MSTP and MD admissions, so one can get a post-interview rejection for MSTP but get a MD acceptance; however, for an MSTP candidate who has interviewed, post-interview MD rejection also results in MSTP rejection (since MD acceptance is required for consideration). On the other had, at Pritzker, Pre-II MSTP rejections get routed to MD-only office, but a post-interview MSTP rejection is the end of the line for both MD and MSTP (post-interview MSTP rejections are not routed to MD office for consideration).**
**This is from memory, and it's been a while, and I can't find my spreadsheet on it at the moment. I don't remember what the policy was for Pitt, or how it works for waitlists. It sure would be nice if they standardized (at least some) of this.