Hahaha. It's tough. You gotta be lucky. Maintaining interest for two can be complicated - for a group of persons with different things they like or doesn't like in a Roleplay, almost impossible. You have to get lucky. 

I noticed a pattern here. In the multitude of posts I've read in the IC, a lot of characters tries to outdo the others. Some posts were quite literally ignored by others, which lead to over shadowing, which lead to loss of interest and to loss of players. ^-^ 

I've run a RP that lasted 2 years, but with a post or two each month max. OOC was chatty, more than the IC, and all characters were kind of friends. Interest had been lost a long time ago, but we just didn't want to see it die. x) 

Anyway. If you lose too many players, you might want to make it so we get to a kind of ''Second Start'' where it would be easy for new players to jump in and meet one another?