What to do with ivy on slope?
Ivy is a real problem in the PNW and other areas, as you know. I don't believe it is responsible for the dead shrub. It kills trees and other growth by covering the leaves which prevents photosynthesis. As you know, this is a massive undertaking. Pulling ivy will result in regrowth if bits of root are left behind. Herbicide might take repeat applications; choose a product that is labeled for English ivy and follow instructions. There are erosion control measures you can employ. Here is a rundown of natural products: https://depts.washington.edu/propplnt/Chapters/erosioncontrolchapter%5B1%5D.pdf. There are also manmade products you can see here: https://www.newpig.com/pig-blue-absorbent-sock/p/4048?couponCode=PLAHOODIE&gclid=EAIaIQobChMIsMS2-v252gIVVbXACh01vAXyEAQYASABEgLywvD_BwE. Planting as you clear the ivy will help, too of course. Another strategy is to use one of the erosion blankets, wait 2 weeks for the ivy to re-emerge and get it again. It isn't a site that will be easy to tend which makes native plants, grasses and shrubs ideal. They need minimal care once established; watering the first year and trimming back in spring are about it.