He doesn’t have to be- Trump is not favoured at the moment, so assuming that Pence would have exactly the same probability of winning once he reaches the general election, it’s still three low probabilities multiplied together before he wins the thing.
Let’s throw some rough numbers into this thing.
74 year old male- probability of death in 12 months (source). 0.032394 Five months until the election, so multiply that by 0.416. Pence is the most prominent Republican who could take over from trump (and he could be the presumptive nominee after the convention), so 0.5 probability of getting nominated, then another 0.43 for the probability of a win in the election.
This gives you a probability of Pence winning of 0.00289731936, or a 1-in-345 chance.
Buying that for a cent on the dollar is still way overvalued.
That’s way overvalued as well. at the moment, her path to victory is:
Biden drops out → she gets nominated at a contested convention → wins Election
OR
Biden chooses her as running mate → Biden is incapacitated before the election but after the convention, → wins Election.
Either one of those chains adding up to a 3-in-100 shot is also tenuous, but people gotta play the long odds, I guess.