Rational people understand the importance of perception in such things. The perception of bin Laden in the Middle East is not that of a run-of-the-mill terrorist. He has a broad following that is growing by the hour. His supporters are steeped in the Mahdi prophecies, and many of them are coming to perceive him to be the Mahdi. If he survives long enough, he could ignite a true "no kidding" Jihad of millions of sympathetic Muslims. What would be their aims? His aims, i.e, to drive the US from the Middle east and to destroy Israel.
Maybe he'll fizzle. But maybe he won't. Only a fool would ignore the possibility that he could inspire a broad-scale militant uprising of millions of Jihadists.
Afterward Islam would be decidedly a minority religion confined, as it were, to a couple of the Westernmost islands of Indonesia.
This is not exactly the kind of thing a Messiah-like figure strives for.