The idea that if Boris had not made it through Covid we'd be all doomed, because he was irreplaceable and carrying an entire party along for the benefit of the country, is preposterous. The party is greater than the man, it was there a long time before him, it will be there a long time after him, it put him in a role and it took the role away.
People voted the unusual way they did in 2019 for two unusual reasons:
1) Brexit had been dragging on because the Tories did not have a big enough majority to see it through properly, so the electorate gave them that majority because nobody else was promising to see it through
2) Boris was shiny and new and Corbyn was Labour's worst error since Michael Foot. Boris could have been almost anybody from the Brexit side of the party. But Boris is no longer shiny and new. Many more people have now seen him for what he is.