Israel can avert the coming destruction by either surrendering quickly to Assyria (“him that smiteth”) or to their God. Isaiah is certainly not equating the two sources of safety. Obviously, it would be better for Israel to have faith in Yahweh. But Isaiah’s point is that Israel chooses neither, instead asserting its own wisdom and strength. That pride will guarantee its destruction.
Gileadi and the Revised English Version translate “palm frond and reed” instead of “branch and rush.” The “head and tail” clearly relate to an animal, and the “palm frond and reed” are representative of plants. It is possible that these terms are used to describe an inclusive category, that is, all animals and all plant life. However, this would not indicate that all life will be destroyed, but rather that the destruction would be significant.