For those still reading along, I went back and looked at Igor Shpilenok's site. It's very high-quality. His pictures of the Kronotsky park are wonderful. See below. Many of them probably show what the Valley of the Geysers looked like before the slide; I'd be curious to see images that I knew were after the slide for comparison.
Kronotsky Zapovednik
Looking one more time, I found a link (under "About Igor") that shows what happened to the Valley of the Geysers. Summary: several geysers were lost, but the "best part", with the stained glass wall and a couple of the larger geysers, survived. Nature happens.
Valley of the Geysers: What Actually Happened
Stained Glass Wall
