"If anything happens to Trump in the next 4 years, Vance gets to be President and then the chance at another term."
It depends:
Section 1. No person shall be elected to the office of the President more than twice, and no person who has held the office of President, or acted as President, for more than two years of a term to which some other person was elected President shall be elected to the office of the President more than once.
ie, LBJ served out JFK's remaining term (~15 mos), was elected in 1964, was eligible to run again in 1968 but declined due to his unpopular actions during the VN War.
If SCROTUS dies in/is removed from office after two years of this term, Vance could be elected twice more.
Kinda sends chills up your spine, doesn't it?