It definitely has. League of Legends is considered a serious e-sport game. Individual tournaments for League of Legends have $2,000,000+ prize pools. If a new bug decided a round of the tournament, it would undermine LOL as a serious contender for this type of attention. There is a terrific business case for investing the time to make this game as stable as possible.
This has actually happened before at official League of Legends tournaments (that is, a fairly serious bug in a serious match). I believe their policy in the case of a serious bug is to re-do the match, but I am not 100% sure.
It depends. If the bug was caught before game of record, you just restart the game. Afterwards, it must qualify as a game deciding bug. If so, the game gets scrapped and the match is redone.
This actually happened last year at their biggest tournament. A well known bug caused several champions to be disabled midway through the tournament. This happens regularly that champions are disabled due to bugs at international events.
