an example for this would be aurelion sol being in the summoner's rift so that he can break out from mount targon. i don't really know the implications of the various fates of characters; jayce and viktor didn't really die, heimerdinger got sent to bandle city and jinx is alive, but ambessa is a tough one since there's no direct explanation for her being in the summoner's rift. perhaps she's in the death realm with mordekaiser? maybe they're changing the rift so that the side that wins lives? (in ambessa's case, anyway - i am nearly sure that one of the devs has already spoken about this in a two hour long video that i haven't fully watched yet)
Moreover, what the fuck does this mean for other characters ala camille, blitz, urgot, renata glasc, etc? Are they erased from canon, or...?
renata glasc might come later after the show ends, considering she was designed after the developers failed to implement silco as a champion - it's not explicitly stated. urgot may yet appear in the noxus show, there were rumors of one of the characters being camille and blitzcrank... i don't know, i'd assume they're going to rewrite his lore or he'll appear / they'll mention him in the next show. twitch and zac didn't appear, but that doesn't mean they don't exist.
With them teasing Swain, I wonder if whatever show they make next is going to be focused on Noxus and maybe Ionia? Or maybe Demacia? Hell, who knows if they're making another show or a movie, I'm unironically reeling.
they've announced that three shows have been in development, with the fourth one in development for a year now. one focuses on demacia, the next on noxus and the third one on ionia, so you got all three right. noxus is definitely going to be a continuation of arcane with mel, whereas i think ionia will include jhin.