Second Civil War? Possible. End of the Republic? Questionable.
Although the start is another matter, another prelude certainly?
But when you get down to that, look at the first Civil War.
I kind of suspect January 6th may be viewed much like John Brown's attack on Harper's Ferry in the future, but time will tell(and who wins will play a factor on that).
But Harper's Ferry didn't start the Civil War, although it certainly was a prelude and warning sign.
Before there was Harper's Ferry, there was "Bloody Kansas" as well, and a number of other things. All clear warning signs in retrospect, but not "the start" of the war.
The other side is the "next civil war" which hasn't actually started yet, is going to be mostly 4th and 5th Generation Warfare, it's going to look a lot more like Iraq or Afghanistan, or even some echoes of the Spanish Civil War.. But reality is, I don't think it's going to get very far. The Silent Majority is still a very real thing, and they're not going to stand for it, and once everyone gets a taste of what a real civil war with open violence/hostility looks like, things are likely going to walk back from a lot of the insanity... But it's likely to get positively nasty before it gets better.