What do you think kills RP's most often?
1.)
Waiting loops.
There are pros and cons to having lenient posting rules and avoiding a strict turn order. Personally, I think the pros outweigh the cons, but only when a lenient system like that is done
right, with a GM that's capable of watching the whole thing and making sure everyone knows who's waiting on who. Otherwise, a group can easily come to a halt because everyone thinks they're supposed to wait for a response from someone else, resulting in no one posting at all. It can really kill a game's momentum, and, while a GM can get it moving again with a bit of prodding, it can be difficult to reclaim the speed that the RP had before the slump. And, when things move too slowly, players are more likely to lose interest and, well, yeah.
2.) Waiting too long for one person to post. I've seen plenty of RP's, typically the ones with strict turn orders, where one person is taking a while to post, and so
everyone has to wait for them -- even people who weren't even interacting with their character and so have no reason to wait for a response from them. It can bring the RP down to a cripplingly slow rate, especially if the person you were waiting for turns out to be a silent drop-out. And, when things get really slow, other players are more likely to get bored with things and lose interest, so, yeah... This is one of the reasons why I avoid strict turn orders. Even if you have a set wait time before you plan to move on without someone, your characters aren't usually all in the same place, and so, there's no reason for
everyone to wait that X amount of time before either you get a post from them or you give up on waiting. Without strict turn orders, I feel like an RP can move at a much more natural pace that keeps people's creativity flowing. But, of course, you have to be careful with a more lenient system, for reasons mentioned above...
3.)
Lack of direction. It is insane how many RP's fall apart so quickly just because the GM didn't give the players anything to do,
especially early on when the players are only just introducing their characters and making a few light-hearted first interactions, leading to a lingering sense of "...now what?" when they run out of small talk. There needs to be something the players are supposed to be doing -- and not just a long-term goal but a
near goal. If your characters are already doing something interesting, then that's fine -- let the story progress where it naturally will. But if your characters have nothing to do?
Give them something. An enemy, an objective -- anything, just so long as there's some sort of direction. Otherwise, your players will get bored, and lose interest, because the lack of anything to do made all their inspiration quickly fade away.
And, in all these cases, I've noticed that the drop-outs that happen as a result almost seem to be a sort of chain reaction. Because, if one player drops out due to just them losing interest, or for personal reasons, but you still have a sizable team of dedicated players, then it's pretty easy to carry on without them. But when you have one of these big problems rapidly stagnating your RP and causing boredom all across the board? Well then, you'll have one player who'll drop out, and then you might have a few more who drop out shortly after that as activity becomes even harder to work through as the GM attempts to work around said drop-out, and then you have more and more players seeing what's happening and deciding to jump ship as it seems to not be worth it anymore, and... yeah. I chose the three reasons I did not just because they can quickly halt an RP's flow, but because that stagnation can lead to a lot of people dropping out at once if the GM doesn't act quickly, thus making them rather difficult to recover from if you're too slow to react.
what is the longest RP you have managed to keep going on Iwaku?
Strictly speaking,
Welcome Back to the Guild, which has been running (on Iwaku) since late December of 2014. I'm not sure if it counts, though, since I migrated it here from the Guild (on which it had been running since long before that), and it wasn't even a reboot or anything -- we just picked up exactly where we left off. The entire player-base is from the Guild, too, and not a single new player has joined since we migrated.
In terms of RP's that started on Iwaku,
Fandomstuck: Fandom Square, which has been running since January 2015.