it’s a whole new ballgame

It really isn't.

Even under your scenario, we have a constitutional crisis. The constitution does not intend for us to live under the rule of a person we did not elect, in fact it exists to prevent that. However, it does not provide a specific remedy for this situation.

Agree 100%.

Nothing precludes the State Legislatures from decertifying their electoral college results. Nothing precludes Congress from doing the same, with the exception Dems are in control.

None of that will have any effect on who is President. Biden would still need to either resign or be impeached.

If the answer to those questions are yes, all involved are disqualified from holding office under Section 3 of the 14th Amendment.

That would not apply in absolute terms like you're implying. If that were to happen, Biden would need to be impeached on those charges first (since a sitting president cannot be criminally indicted). Only upon conviction would he become ineligible to hold office.

If that is the case, nothing they have done since committing those acts would be considered official, including certifying the election.

That's just not true. None of this would apply retroactively. The election was certified. That's it. It's final. Everyone would know that they committed massive fraud to steal the presidency, but all of their prior actions will stand.