We'll be able to tell if 2008 wasn't in 2010.
I disagree. People say that 1968 was a realignment, but the GOP didn't do so well in 1970. Congressional elections are, I find, not a good way to tell if something was a realignment. The Democrats could do poorly in 2010, but landslide in 2012/2014/2016. Presidential elections matter a lot more in determining a realignment than Congressional elections do.
I actually know very few people, in academia, that claim 1968 was a re-alignment, after the fact. It is very hard to tell a realignment at the start.
It won't be a question of the Democrats doing poorly, but how poorly.
Indeed. Many experts see the election of Carter in 1976 as a classic Democrat victory in the model of any post New Deal election. The Deep South returned to the Democrats after the civil rights upheavals of the 60's. CA, IL and MI were Republican in that close election.
For those experts 1980 is the realignment. After that TX, AL, MS, and SC have been strictly GOP for President.