While the date can be (and has been) changed, states have their own deadline for certifying results. I don't think any have passed that mark yet, and Alaska's senator is still unknown. All of the winners are still technically predictions. Some states (like Georgia) often have a run-off election in January.

It can all be done, but has a lot of moving parts. It might be easier to keep Congress out of session unless certain circumstances are met, but I can easily see that being abused for the same partisan reasons.