And then what? Once the mob was cleared out, they would have resumed. There's a chasm between disrupting proceedings and actually taking over a country. The latter also almost always involved having control of the military by the way.
It might've been a short civil war, but if Trump had gone out and marched with the protesters like they thought he would and told them to stay in the Capitol building, you would've immediately created a situation where government business is suspended and the commander in chief is at direct odds with the military's constitutional obligations.
There was, and has been, a soft coup ongoing since that day, since the president at the time refused to issue any direction to the military and situation only started to be resolved when Pence took defacto command of the executive without invoking the 25th amendment. That process has been ongoing since then.
Remember Trump is already commander in chief, so has power 'by default.' He just needs to create a situation where that status quo remains, either by creating a situation whereby the right people are willing to disregard the election results /or/ the constitution directly.