I remember riding the Haunted River on a day with moderate rain. The ride's inside scenes leaked rainwater in numerous, and I do mean numerous, places. Quite a lot of rainwater. It seemed to be beyond the park's capability to keep up with the scale of the issue. This was back in the 1980s and early 1990s. By now I can't even imagine how much patchwork-over-patchwork-over-patchwork remediation of various kinds has been visited upon that structure.
How long did the original crews designing and building the mountain expect it to remain in the park in the first place? If you had told them in the 1970s that their work would have multiple lives, adapting to new ride technologies and elevated public expectations, turning into a danged fire-spewing volcano in service of a totally unique, record-setting, space-age roller coaster ride, and then living to see the impossibly futuristic year 2019 -- don't you think they would have been absolutely thrilled? I do.
I really doubt the structure's anticipated service life back in the 1970s was something on the order of 40 years, and honestly I am a little bit surprised that the Intamin ride system built around it made it to 20. (I am similarly surprised by the Flight of Fear rides' continued existences, though that is a completely different story for some other time.) Kudos to the park for keeping Volcano's unique but odd combination of papier-mache scenery and quirky first-two-thirds-of-a-coaster upright and operational for so many years.
Keep in mind that Cedar Fair has a park with TWO structures that are similar in construction to Volcano's (steel I-beam infrastructure, rebar based outer form with mesh, and a 1-2 inch layer of sprayed concrete on top of it. And they are both older than KD's mountain.
Knotts has a mine train attraction and a log flume attraction that are dark rides or have major dark ride components to them. Both received major refurbs to the "fake rock" facades, and all new dark ride scenes for them.
I certainly don't know what will be replacing Volcano; but, the potential to extend the life of the mountain structure certainly exists within the CF chain. Matter of fact, this would give KD the best opportunity for a major refurb on the mountain structure without the coaster going in - through - around the outer shell.
Keep in mind that what the park has left is just the outer shell of what was "The Lost World" ride complex. The interior had multiple "caverns" and "tunnels" that made up the scene areas for the Haunted River flume and Doozy/Smurf mine train. Some of those "caverns" for the Haunted River scenes were massive, having ceilings of around 30 feet. Even the "Time Shaft" Rotor flat ride had a "rock tunnel" queue line and "cavern" for the ride itself.
KD certainly has the opportunity to make the structure back into a mountain, with or without another coaster attraction on that spot. Plus, with the mountain already gutted, the park has a blank canvas to work with whatever they come up with in the future.
It all comes down to whether the mountain stays or goes with the coaster.