It's amazing that it can get this messy. A president-elect dying in 4 months is not that unlikely: 65+ has a probability of dying about 1.5%/year [1], so 0.5% that they die between November and January. For a 74 year old it's even 3.6% and 1.2% respectively, for a 77 year old 4.5% and 1.5% [2]. And that's not even considering that there is a lot more stress in that time.<p>[1]
<a href="https://upload.wikimedia.org/wikipedia/commons/4/47/Excerpt_from_CDC_2003_Table_1.pdf" rel="nofollow">https://upload.wikimedia.org/wikipedia/commons/4/47/Excerpt_...</a><p>[2]
<a href="https://www.semanticscholar.org/paper/United-States-life-tables%2C-1998.-Anderson/786695111e5cf0ea6153bf4c28a43699bdc1edc2/figure/2" rel="nofollow">https://www.semanticscholar.org/paper/United-States-life-tab...</a>
Despite technicalities, what matters is what the mass populace and people in government accept, and obviously that means the VP candidate on the slate takes over.