Biden would be elevated, it would seem fairly certain. But I have seen comments saying that whether Obama was “never” eligible could depend on whether he was ineligible due to intentional fraud (hiding foreign birth), in which case his ineligibility would be retroactive to inauguration, or ineligible due to a “case of first impression” SCOTUS ruling that he was not NBC due to having a foreign citizen parent. The latter type of ineligibility might not be retroactive. Worst case it might be applied only prospectively, giving Obama a Mulligan! (Heaven fore-fend!)
Another possibility is there was a change to the original Hawaiian document when Lolo Soetoro adopted him as Barry Soetoro.
Finally, I am not sure Obama's mother was in US at alleged date of Obama's birth. She could have been in Kenya or Canada, where she began classes shortly after the alleged birthdate.