Iran is well aware that this is a Mossad job. They're not going to start attacking US bases in retaliation - that would just hurt Iran even more.

The point of this assassination is to make it harder for Iran to restart even with a softening US stance. Iran obviously has other scientists who can pick up the baton, but don't underestimate the amplifying power of a visionary, and the impact on morale when you lose someone like that. You've also got the gnawing fear factor of anyone who succeeds him, having a giant target on his back.

These are classic tried-and-true intelligence service tactics, and they work well.