They’ll be sending more.
A lot more, everywhere, and all at once.
It takes more than one EMP to end a civilization.
That’s like worrying that they’ll send a nuke via an glow in the dark mule. They have much better and harder to stop, detected, and verify methods it’s insane.
Any major EMP strike would be considered no less seriously than a nuclear one anyway, it’s not worth worrying about.
I think this whole thing is goofy and overblown. Yeah we need to shoot these down, but it’s not some major coup on anyone’s part.