We won't have to wait long. Biden's infirmity is becoming unmanageable for his handlers to the point of yanking the video feed on him during live broadcast when he goes off script with "I'm happy to take questions".
Since Harris is on deck and warming up already (making Presidential contacts with foreign leaders), I believe the only two things holding the puppet master back is optics of Joe failing too soon and getting the crisis resolution moving parts all in place.
Never letting a "crisis go to waste", the process of activating 25th amendment would naturally come after top choice: something like an announcement of resignation _or_ assassination. Death by "Domestic Terrorism" would be the coup participant's wet dream come true.
IF they can plausibly manage it, how many here think they'd hesitate?
Jill really ought to be very, very careful about keeping her husband away from grassy knolls. Collateral damage, messy for her and her "Doctor" ego-ridden self...
Choosing a VP if a President was removed from office....
I believe it would be a joint decision by a committee made up of Senate and House members, followed by a vote of both legislative branches for approval. A quick search on the interwiz says it would be the speaker of the house. Either way it doesn't matter as Harris would rule with a iron fist.
Remember my predictions for 2021? 2021 will be 10x's worse than 2020.