If Trump is alive and healthy enough in 2028, he will try to run for a 3rd term, or rather, unconstitutionally refuse to leave office and call it "running again". If Vance becomes president in the next 3.5 years, he will run (legally) for a 2nd term, and he will lose. That's why "not for long".
If trump croaks jd would only be in power till midterm elections, immediate impeachment
Hey google, when's the last time a presidential impeachment actually led to a president being removed from office? Three presidents have been impeached, although none were convicted: Andrew Johnson in 1868, Bill Clinton in 1998, and Donald Trump twice, in 2019 and 2021.
Hey Google, when's the last time there was an full fledged fascist occupying the white house that led to an entire political party being wiped out in midterm elections? If the the dems take the house and senate they will have the votes to impeach, convict and remove. This is the peaceful option.
I think if the US had a parliamentary system, Vance would likely not last as long as British Prime Minister Liz "head of lettuce" Truss. At that point one could hope for an election. If not, then for a faction to solidify behind Kinzinger. More likely someone like Kemp though.