I don’t see anything about this being bannable, and I’ve had plenty of people leave my keys this season, it’s pretty much expected that people will leave if there’s a wipe or anything.
I’ve seen people wipe on a big first pull and then leave a few times as well.
If this isn’t a thing, would a false report still be actioned on?
Very curious about this since someone I know got a temporary suspension over this apparently, but I’ve had it done in my keys consistently too?
It’s actionable if a pattern of malicious intent can be established, yes. Leaving just after the beginning timer expires or just before the first boss is pulled, as examples.
Leaving after a wipe or two wouldn’t necessarily be considered such as they are putting in some effort to complete the key.
Sorry! The “it” in question being the person leaving, not the person reporting.
Leaving keys is not bannable or actionable in any way. Now if someone you know said things that might not have been so nice they can be actioned for that but not for leaving a M+ key early.
I would think they would need to see a lot of this to action someone over it. See a pattern of the same thing, not just getting suspended for leaving a M+
My follow up question would be:
Shouldn’t the first person to leave be the one to be punished, not the person reported?
It seems like a tank in our guild had some bad runs and left after a few pulls and it got blamed on the other guild member and he was reported despite not being the one who left.
I’ve also ran with that person and had this happen, nobody in the group was happy with it, but it looks like only one person got reported?
I’ll take the suspension in his place, I don’t care that much, but the person who actually left should be the one punished imo, not just whoever gets angrily reported
Who had the stated intent to trash the key?
If there was no communication threatening to brick the run, it’s pretty much non-actionable. Anyone can report as much as they want. Without concrete evidence that someone is being willfully malicious, the reports will be ignored.
Read the opening paragraph of the support article.
If you encounter behavior in chat that demonstrates malicious intent to sabotage the run of your Mythic+ group, you can report the player by using the right-click option in-game.
That’s it. That’s the only reportable “ditching an M+ run” behavior. If you didn’t do that, 1000 reports wouldn’t matter.
Like Ekon said unless you have a pattern of leaving M+ early to cause issues with other players this should not be something you get punished for.
Everyone has bad runs and if you leave after a couple wipes no one is going to suspend you for that.
Yes, that’s what I said. 
The pattern of sabotage would be the determination of account sanction.
I assume pattern of sabotage could be leaving multiple runs in one night?
So if I queue with that guild member who quits after 1-2 pulls and he does it more than once, I’m risking my own account if reported since it might be established as intent?
Not unless blizzard see’s communication between you and that guildie about doing this about leaving early. You would not be at risk if they do not see the pattern on your part. Honestly a big reason I do not like pugging high level M+ keys. Just never know who you will get!
The guild member apparently just got it overturned as he had apologized to the person in whispers and offered to help on another key, but there was no intent to brick.
There’s definitely more to it than just stating intent in game, and we definitely had no intentions to brick anything, since we were equally frustrated with our guild member who had quit.
Is there an established criteria for when it’s actually okay to leave a key?
If you have a guildie who seems to leave keys often I would put them on ignore and not group with them.
No established criteria I can think of, but if the group is struggling and you wipe a bunch of times. No one is going to come after you for leaving, Just do not say anything foul or anything bad before you do. You can be actioned quicker for language then finding a pattern of bricking peoples M+ keys.