If Biden doesn't die, He'll intentionally resign so he'll be remembered as the guy who "paved the way for women leaders in America" I feel that would be a hollow victory for the left. It's not a win if it's by default. I would rather the first female president be inaugurated legit through the electoral process.
Harris will become President when Biden leaves office, And Biden will leave office in his first term. Age or health will force him out of office, Not to mention being forced out by the Democrats. Harris will complete his term, But will not be re-elected. This assumes that the election on 2020 stands.
The election is gonna get overturned, Putting Donald J Trump back in the Oval Office, Therefore shutting down any nexus (Joe Biden)) that senator Harris has to the Presidency. That amongst other things (like nobody in their right mind wanting her as President destroy any chance she has of being a female President. Forget about the first one.
In terms of Biden's health, He seems to be doing decently, And the president of the US has one of the best medical teams of anyone (I mean, They're the president), So unless Biden has a major health issue, It's unlikely it'll affect his seat in office.
In terms of Harris succeeding Biden via winning an election, It definitely could happen, But it's unlikely. Recent vice presidents have had trouble succeeding their presidents. Ford lost in 1976 after Nixon resigned, Mondale lost in 1984 after he and Carter were voted out, Bush Sr had won in 1988 but lost in 1992, His VP Quayle failed to be nominated in 1996, Gore lost by a slim margin in 2000, And Cheney and Biden didn't even run at the end their president's 2nd term, And even if Pence runs for president, I don't think he'll do well, Especially considering Trump will probably run in 2024. I could see Harris being able to beat the odds, But recent tides have shown America isn't interested in a vice president climbing up the ladder.
So overall, There's some chances for Harris to succeed, Whether expected or unexpected, But I don't think it's likely.
Women can be placed in a constitutional united state inside the executive office or outside the executive office simply by using a title that creates all women equal without judicial prejudice.
One term would be Presadera of the united states of America as a woman is strategically place in a legal posture of constitutional union connecting her to all woman. Not just in America but in the world as a single united state. A female who speaks on behalf of all women
as she is a witness by basic principle to those who are female in gender.