Firstly, huge credit must go to the fire fighters who miraculously managed to keep the fire to this one building, had it spread elsewhere in Spain it could have been so much worse. It looks like they got it under control relatively quickly. And it is another blessing that no guests were hurt, kudos once again to EP for their evacuations.
I still can't quite believe that we have had a second major fire in five years. It really is gutting. Diamond Mine was such a beautiful walkthrough, something I would do once on every visit. A complete escape full of charm. I am sure it will return but retaining that same charm will be a challenge.
Losing Alpenexpress and Tiroler for this season and maybe some/all of next season is also a huge blow, two brilliant family attractions. I'd imagine the rides can be re-built fairly swiftly once all necessary demolition and clearance has taken place, as they'll only be partially damaged in the sections that were in the building. I guess it depends on whether or not they want to get them back ASAP or whether they want it all to re-open fully themed.
The knock on effect of this should not be underestimated either. The Scandinavia/Pirates fire most certainly delayed other investments across the park by at least a year. I suspect the same could be seen here, as there will only be so much construction resource available.
Finally, as others have said, Geisterschloss must be a huge concern. If that was to ever go up in flames it could take out so much of the park as there are so many connected buildings. All of Italy, some of France, one side of the German Alley, the Magic Cinema. It does not bare thinking about.