I'm with the slow decline crowd. I think number reported will still go up a little but their average age is getting older and older by the day. They have pressures on many fronts that have been brought out (low youth retention, not enough men to take low level leadership positions, reactionary changes to doctrine, apathy among members, media issues). But, historically, they've been able to overcome such things.
I believe they have enough wealth to withstand the slow shrinkage. Combining congregations and selling the KHs is going to keep the cash flow going for quite awhile. I don't believe they're losing money on literature because if they were, they'd stop.
Short of a black swan event, they will follow the path of many non-mainstream religions before them and slowly fade to the outer fringe. But, I don't think it will happen in my lifetime (I'm in my early 40s).