My guess is this is what will happen:
1. Trump will nominate somebody before the election that gets conservatives and fascists excited to vote for him.
2. McConnell will say the Senate will vote for the nominee after the election to protect swing-state senators.
3a. If Biden wins and the swing-state senators lose reelection they'll vote for Trump's nominee.
3b. If Biden loses, regardless of what the swing-state senators said before the election, they'll say "the majority decided" and vote for the nominee.
3c. If Biden wins, but swing-state senators win reelection -- it'll be trickier for them, but Trump's nominee will squeak by with about half of the swing state Republicans + Joe Manchin + Pence, if necessary before January.
Either way I don't expect Republicans to not vote for a conservative justice. They are well aware that their numbers are dwindling over time as Silents and Boomers die off, and their party alienates people who would otherwise be young conservatives with their far-right fascist sympathies. The rewards are too great for them not to sacrifice some of their people, and swing-state voters depend on GOP voters as much as they do "independents" and "moderates."
4a/4c. Biden wins and doesn't do anything to change the courts. People are disenchanted with his presidency as it does nothing to address the current crises and the U.S continues the trends it has been going on.
4b. Trump consolidates his control over government and empowers fascists.
5a./5b./5c. Tom Cotton becomes president in 2024 as a counter to a threat of growing calls for localized socialist insurrections/syndicalism, and the incompetence of Biden/Trump to address the crises. He brings in coordinated fascism unlike Trump's incompetent, uncoordinated pseudo-fascism. The U.S starts the path toward balkanization as many regions are repulsed by Tom Cotton's more competent fascism.
6a/6b./6c. By 2035 at the earliest thru 2050 at the latest the U.S has balkanized into different republics after a warm (neither cold nor hot) pseudo-civil war. Some states join Canada (whose population has ballooned with refugees), but most create/join their own federations. In the interim roughly 1% (~ 4 million) of the U.S population dies from the warm civil war and its effects. More people die from the camps at the border with Mexico, but the number remains unknown for decades. A third of the country by population are controlled by fascists. Meanwhile the world is in disarray due to the failing of American hegemony. China and Russia start spreading their influence in their regional spheres, but they can't replace the U.S as a hegemony. Europe also starts to fall apart if it can't reform.
That is the future the political-bureaucratic class and capitalists have handed us.