Yes, but they can - and do - die by the droves. Been there, seen it. I had level 8 assassins get killed by level 2 heretics, and not just the oddball one.
While I think it is perfectly all right that some figures should be hard to assassinate, there are others where I wish this were not so. Heck, a maxed out assassin has only a meagre 20% chance against an Inquisitor, units like priests, merchants and perhaps other assassins (in RTW - not BI though, a zero-skill assassin has 95 % against a maxed-out one, but the hard thing is actually finding them. But once you did, at least you got rid of the bastards) should be soft targets.
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