It's about time to add Coil story mode, isn't it ?

[Tiggy]

MMO usually fail when they catter to hard to once side of the player base totally ignoring the other or when they never decide what to do. And I have high doubts a MMO would fail because of "no rewarding end game" alone. there are MMOs without any relevant endgame and still going.

On the other end, FFxiv 1.xx didn't fail because of whatever endgame might have been back then but because the game plainly failed to see what the players wanted, or so they said themselves.

I would say
A) You need to do some more research on why MMO's fail to gain traction and either die or revert to a f2p model because end game is a very large factor.
B) FFXIV is arguably the worst big budget MMO to launch in a decade so yes it had other problems than just end game. That doesn't necessarily mean many others doesn't fail due to poor end games.

I think you underestimate the effect the end game crowd has on an MMO in a big way.