Two issues with that.. First they said libertarian, not the GOP or alt-right or anything. Libertarians are the extreme opposite of authoritarianism. They beleive in either small govt or an disempowered central govt... so your characterization is wrong there.
Second, if they are to team up that is only possible if their views meet in the middle. So you would now have left-leaning centrists and right-leaning centrists teaming up... this is exactly why I say it wont happen, both sides wont change their views, and without changing them they cant be compatible as their votes would oppose when keeping to those views.