Coming in here from the sidelines, as I've been disinterested here lately, I have a couple opinions. To run through the list...
PbP has always had attrition in general. One of the major advantages of LEW was that it somewhat blunted the effect of attrition since characters were persistant and you could recruit from a pool of players. Still, it's bound to happen. How many characters on the first five pages of the character thread are still active?
For one, enworld was terribly slow for a couple months this year. It frustrated me so much that I delayed my Red Hand of Doom game for 3 or so months before I was able to continue the adventure.
Then 4th edition coming out. A lot of people like it more, and would rather be playing that, regardless.
And L4W coming out. This probably has a somewhat limited effect, but it's still worth something. I'm sure some players, when confronted with a choice because of their limited time, would choose to make a character for a persistent 4e world at the beginning rather than a persistent 3e world at the figurative 'end' of the edition.
The mega-adventure really was the elephant in the room as someone put it. Having all the games floundering around (and run by one GM mostly?) really messed with stuff. It played against the strengths of the system in some ways by doing that.
Winter is always slow. Christmas season especially. That's some part.
Throw it all in a basket along with LEW not being featured prominantly on the forums (it used to be high enough up that when you looked at the general forum list you could see it on initial load, but that's not the case anymore), lack of character approvals, and some of the other issues and you can see how things would flounder.
Plus, character approval has always been a bit of a pain. When activity was high, it's problematic because there's so many to approve. Even when things are not so active, approving characters takes a great deal of time, making sure every single rule is followed correctly. It also adds a certain amount of startup time for the players wherein they have to wait quite a while to get started. You can't just jump into a proposed game very easily.
Oh, and on another point, enworld really doesn't havea lot of good play-by-post features that can be there. A dedicated messageboard could have in-line dice-rollers, access to view character sheets from the player's posts, and a lot of other stuff. Sure, we can get around it, but all I'm saying is 'it could be better'.
As for suggestions... Well I can see reasons to try to continue on. There's no reason to stop the game for people that are still enjoying it.
I would somewhat recommend a merger of sorts. I realize that thematically this doesn't make much sense, and some players would dislike the idea, but merging LEB and LEW might do some good. You would have a combined player base using the same system.
People that wanted to stay in LEW could, or you could merge into LEB following some guidelines to make the character line up. I'm not sure how much people would benefit from that though, as it probably won't solve any of the core problems.