Depends on the people you roleplay with. I have the honour of calling some people friends on this forum, and one of the requisites is being a 'Roleplay Brick'. Someone who will never give up on a RP entirely, no matter how long and drawn out it gets. I believe it's the GM's decision as to when it is finally laid to rest or whether it's on a break or what. My advice to anyone wanting to build a long lasting roleplay is to build long lasting relationships with people who like the same things as you. A science fiction roleplay of mine has been going for just under three years, through three iterations and Guildfall, because of rock solid support from some wonderful people.