I'm going to give my honest opinion here, but that is a much more complicated issue than "He's an asshole".
First things first, it matters if it was ranked or not - in normals two top isn't a big deal, so he should have manned up, though honestly, why not send the two top bot and him top? It's not like top is fundamentally different from bot, it's just who plays there. You couldnt reasonably expect him to go solo bot against an ADC and Support if he was just ADC.
Which brings me to the root cause of the issue. The two people top thing - If they wanted to both go top, they needed to make that abundantly clear and have a reason why behind it. Were they going to shove the lane? Or was it just two assholes who couldn't agree so they both went there?
I would hate to be stuck bot alone because two people couldn't work out their issues and let one person go top and the other come bot with me. It guarentee my loss of lane, especially if I had already picked a "standard" bot champion. It's shitty of your team to do that to that guy.
As the jungler, you should have probably pitched a tent bot in this case, because of how much help he would need to just stay in any way even in lane. The enemy bot would probably push him to tower really quickly, he would lose farm, take harass and eventually get tower dived. I'm not condoning his feeding, but to him the game was already lost because of the decisions the rest of you made.
So now, he should not have fed, and feeders suck and it's good that you reported him. But if you don't want people to get upset like that and feed, its a good idea to not put them in terrible situations like that. Playing against the meta is fine, if you are doing it as part of a strategy. If the two top people had facerolled, taken a tower or two really quickly, ganked mid and pushed it over then continued to dominate the game - that would work out wonderfully. If the two of them just wanted to lane together, they should have got bot, so it was 2v2 and 1v1 in the lanes. This way the other guy would have had a chance. If it was just two people who couldn't get along and both called top, so fuck the rest of the world, they should have been reported two, because they are just as responsible for ruining your game as the other guy.
And then, as I said, if they were being impossible to deal with, it did then fall to you as the jungler to keep bot lane viable. Clear your buffs then go support him, occassionally popping off to take golems or something. But you really can't expect him to be a happy positive player when he is 1v2 and the rest of the team isn't doing anything to help turn the situation into something good.
Moral of the story - people get upset when they think they are going to lose. Raging and feeding or afking is always bad, but often predictable. If you really don't want it in your games try your best not to provoke it. Always try to make sure everyone has a chance in lane and give people advice or help if they are falling behind. People will rage and they will feed if they feel like there is no hope - and this is especially true if they think it is their team's fault (because they are trying to punish their team). Always try to look at the human behind the rager/feeder and if you legitimately try to talk to them and calm them down, it really helps. I've talked a ton of people out of AFKing or feeding by just telling them we can still win and offering ideas for tactics and strategy. Give people a plan to follow and most of them will. They don't really want to lose the game either, they just don't think there is any other option.
As for your question, if the guy does this a lot, expect it to take around a month from the first time he was reported. If it is a rare thing for him, he may never get banned.
