Is no longer blind. The League didn't exist. Noxus didn't invade Ionia. Lee Sin didn't burn his eyeballs out to protest a rematch for something that never existed. He never wanted to become a summoner, because they no longer exist. He is now simply a blind guy that just kicks ass for no reason.
Years later, hoping to atone for his crime with martyrdom, he set himself ablaze as a protest of the Noxian occupation of Ionia.
Has nothing to do with the League; he's just Ionian Gandhi. Whether a League match or a battle drove out Noxus is immaterial to burning out his eyes.
The rest of his lore can be very easily rewritten to exclude the League. He was training to be a summoning mage (ala Skyrim summoning, not LoL summoning) but got bored with the pace, so he tried to summon something on his own and killed a village. As atonement he went to the Shojin monastery, but then set himself on fire to protest Noxus' occupation of Ionia. He galvanized Ionia to fight back; they drove out Noxus but not before Lee Sin lost his eyes.
The only thing he really needs is continuing motivation, but that's a problem common to almost all champs post-League, and I'm sure Riot will figure it out.
