Vance does not have the cult leader credentials. If he pulled a "Let's take Greenland" out of his ass, he wouldn't have the same spell to keep 30% of approval.
That's why many authoritarian regimes fall after the death of the charismatic leader.
And yes, the root cause of Trump appearing in the political scene go beyond himself and point towards structural problems of US society. But now he has this power, it's a fact that his death will cause a great loss to the political power of the MAGA movement, and it'll be very hard for any successor to keep this coalition in power, specially considering they're already fighting among themselves.
"Charismatic leadership" is an expression often used in political theory to describe leaders who are able to agrue a personal following and use it for political gain, in a level unlike that of most politicians, to whom support is way more conditional.
It' doesn't necessarily mean the same as "approachable" , or anything that "charismatic" usually is used to describe. It's been used to describe figures as awful as Hitler or Mussolini.