I went with a transitional presidency. I wholeheartedly agree with the 1896 parallel especially if Warren winds up as VP.
Like President William McKinley, a President Joe Biden dies in office early in his term with his Veep serving the remainder (although not as a result of an assassination). I hope that whoever serves the role of a Theodore Roosevelt shouldn't be as squeamish as he was about effectively serving two terms but only running for one in his own right.
I would hope and think that Biden serves a full term but steps aside in 2024 in order for his VP to pick up the reigns. Who then hopefully goes on to serve two full terms.