This wouldn't be a problem if people don't look down on Free roleplay so often. 

For example, I used to be part of a Free RP on oldGuild that lasted for [i]years[/i] across a couple installments. Being in Free, you could post one-liners if you felt that's all that was needed. But you wanna post paragraphs? Nothing's stopping you. The GM ran the RP under the idea that "Free means post whatever length you want; there are no guidelines or restrictions", which is an idea I've carried with me since whenever I poke around Free RP's. There was great variation in post length and it seemed to result in everyone being as comfortable as possible. Even I remember posting occasional one-liners followed up with three-paragraph posts, depending on what each situation called for. Theoretically, there is no max post length for Free, so really any Free roleplay could turn out like this one.

That said, I kind of have to disagree with the notion that this is what [i]causes[/i] RP deaths. As someone who's been GMing for years and working out countless kinks in activity flow, I'd have to say that most holdups come from dropouts, confusion regarding who-should-post-when, not knowing where to take the plot after a certain point and, well, a number of things really - but hardly has it seemed like post length was responsible for any of it. Free RP's die too, you know. Even TJA, the Free RP I was talking about before, had its slow moments. Remember how I said it spanned "multiple installments"? Yeah, it died a few times, too, despite the staggered post lengths. Really the only thing that kept it going was the determination from the remaining members of the group each time to pick up the pieces, fix the damage, and keep going. And really, I think that's all that any RP needs. Almost every sudden RP death I see is caused by a minor problem causing a temporary holdup that no GM or anyone else in the group attempts to work around. A lot of RP holdups are easier to fix than many people seem to think.