What if the attempt to use the alternate slates of electors and/or have Pence declare Trump the winner in the last election had occurred, and it wasn't overturned by the supreme court. Democracy lost - at least temporarily - or no?

Jumping in for a moment, this isn't something that had any reasonable chance of happening.

While some of the alternate slates of electors were utterly fraudulent, enough of them (like the ones from Nevada and Pennsylvania) were qualified on their face that they would only be effective if a court ruled that Trump had one the election. And Pence had already declared - correctly - that his role in certifying electors was ceremonial, not substantive. Nor would this scheme even have worked if Pence had gone the other way, since there really is no legal framework for state legislators to change their election laws after an election has taken place.

I think the point BHM is making - and I agree with him - is that whatever the plans were of the Proud Boys and Oath Keepers, they had no actual real-world chance of allowing Trump to retain the Presidency. They're still guilty of plotting to overthrow the government - but their plot was so foolish that it couldn't have worked. It's like a group of bank robbers who plan to bust open a nigh-impenetrable vault using a crowbar (which we postulate is physically impossible) - the valuables in the vault were never in danger, but they're still guilty of plotting a bank robbery.