Alliance leaders r4 and r5 are offline, can R3 do something to take it over?

I know that R4 members can replace the leader if the leader is offline for 7 days. I don't know if R3 can do this as well. If you need to take over as an R3 you may need to message the developers and ask them. Try the contact option that is found in the 'Support' sign in your city next to your base building.