Of course, this analysis is grossly oversimplified and demonstrates an entirely underdeveloped sense of history. Convert baptisms have risen and fallen in the past due to a variety of factors: wars interrupting missionary service in the '40s and '70s, 18-month missions in the '80s, et cetera.
To predict the extinction of Mormonism or the failure of missionary work based on a relatively short trend of declining conversions is short-sighted. If you want to accurately predict the future of missionary work, you have to take into account historical patterns, current church initiatives -- oh yeah, and you have to be God.
I do think this is an important discussion to have, and I plan on investing more time in examining the external problems facing the LDS missionary program. But I also think it's important to put all of this in context.