Unless we fumble horribly the second half of the season, I would put him in the same group as Pep and Lucho already, even if we don't win UCL.
It's clear nowadays if you don't have money to spend on players you won't be winning shit against PL teams in UCL. The amount of money being spend on building teams have increased massively past decade. It is fool's hope to think we should able to compete just because we have the best academy in the world.
Once I see us spending 100M+ in a transfer window for players we have actually been hunting all along, I'm not blaming Flick or anyone else if we get knocked out from UCL. As long as that team is actually a proper team.
Even if Flick never wins UCL with us but still beats Real in domestic competition on a regular basis, he should be remembered as one of the best in this club. Because his work and development on players have been crucial when we eventually win that UCL with some other coach within the next decade.
Both Xavi and Flick should be remembered as the coaches who gave this team some credibility in one of the darkest periods of club's history.