1. It is unprecedented that a YPDA Agong would resign. While provisions has made for such a situation, more often that not, either their 5 years ends or they pass away whist in office.
Normally, they elect the next in line on the order of seniority that was formed in 1957.
4. The second in line? the Sultan of Johor. Yeah, him.
That would itself is unprecedented and unless agreed upon the Sultan of Johor, will be a huge insult to the state.
That it would mean the crown prince of Johor, Tunku Ismail would be regent might be bad news for the state government tho...
The public usually just calls him Agong for simplicity sake.