I don't, but neither do the players in this hypothetical scenario. They're losing their League investment if they leave, so the benefits must be more attractive in order for the players to decide to leave. Given that ARAM would be as popular as SR in this situation, I'm assuming that Riot would be supporting ARAM roughly as well as SR. As such, the choices would be to a) stay with League for decent support or b) leave League for possibly more support. My guess is that the majority of players would stay in that case.
Players would have to abandon their investment into League because they'd potentially be switching to a new game managed by a different company. Generally, you can't bring account properties (e.g. IP, RP, champions) with you when you move to a new game. Of course, this is assuming that players play either League or the ARAM-focused game, not both.
Correct, which is why I haven't used any specific numbers. All of this is hypothetical.