From what I can tell, most folks on this site are Sanders supporters. So is there any truth to this article?

"Bernie Bros warn of ‘massive exodus’ if Democrats nominate Joe Biden"

I know in 2016 while the Democratic base voted for Hillary 89-8 over Trump with 3% voting third party. Sanders supporters did vote for Hillary, but by a 75-12 margin with 13% voting third party. If this about to happen again?
It's high past time that we start electing Americans to congress and the presidency who put America first instead of their political party. For way too long we have been electing Republicans and Democrats who happen to be Americans instead of Americans who happen to be Republicans and Democrats.