Rage Quitting an insta ban?

Alright, I was playing a game and about 8 minutes in, the enemy team complained that their mid, a Ryze, left. Apparently, they warned him not to leave and he rage quit. I shrugged it off as "I'll report them later". Until they asked for us to report him. Okay, sure. And again. And AGAIN, SIX MORE TIMES. I spoke up and said that while what he did was reportable, we really didn't need them constantly asking us to report him after every fight, could they stop. It became a discussion that they needed us to report him so he'd get banned.

When I commented that he likely wouldn't be banned unless this is something he did frequently, it became a FULL GAME chew out, apparently, from their adc. I muted them when they started in but their team frequently complained they were still chastising me about how I was wrong and they were right and he'd be banned, even after he returned for the last 10 minutes. End of game and they immediatly started "Ori, just a thought" and I left.

That said, is rage quitting once a perma ban because they were warned by their team not to?