Q.Viability of butterfly bush
I have a butterfly bush that was planted last year. At this date, May 2nd, the bush has not started to show any green. When I take a limb between my fingers it is not brittle, rather bends easily. I live in Zone 6 and most everything else is showing signs of life.
I would give the plant more time; especially since the branches sound alive and viable. You may watch at the base of the perennial. Often time it will grow from the root, not the remaining spent branches.
https://www.gardeningknowhow.com/ornamental/shrubs/butterfly-bush/butterfly-bush-care.htm