You know the Constitution. Can you please affirm the info in Post 31 and my response in post 45? Or if not, do you know what rules apply here? Thanks.
It's really more a question of Missouri state law than the US Constitution. If Talent defeats the widder woman in this special election (which it is, despite the fact that it's held in the regular November election), he's eligible to be seated immediately.
The problem could be that Missouri law requires that the Governor certify the election results of any special election, and since he's a Dem, he might just refuse, especially if it makes the difference as to who controls the Senate.