Hypothetical sanctions?
 

If sanctions put in place hypothetically prevent Aeroflot from flying EU or USA would existing passengers likely be placed on another SkyTeam carrier by Aeroflot? Any precedence or similar situations in the past?

I don't think there is any precedent like that and, if it happens, I doubt SU will be in a position to transfer their pax to other Skyteam carriers (or any carrier). If SU is banned from flying to EU and US, then all EU and US carriers will be banned for flying over Russia and so the impact would be so huge (especially for EU carriers) that you can be sure that it will never happen.

Hypothetical sanctions?
 

Won't happen.