My answer would depend on your definition of "terrorist leader." Mohammed Atta is now being referred to as one of the "leaders" of the 9-11 attacks, but that didn't stop him from killing himself.
If you mean the "leaders" such as Bin Laden himself, my comment would be that cowards like him always get their suicidal sycophants to do all the dangerous work.
As for terrorists having access to smallpox, I think most experts agree that they probably do. I don't include 60 Minutes in the "expert" category, but this is the only link I have on hand: '60 Minutes': Iraq Has Smallpox
This other one doesn't mention smallpox specifically, but it's close: Bin Laden 'Has Biological Weapons'