I think that there will be a drop price wise if film should ever disappear. As long as Film was the thing the pros used Nikon SLR's where as steadily priced as Leicas nowadays. I remember a collectors Principle "the possibility to take photos with a camera fixes its value and finally its price". (I remember how they labeld broken cameras as "for collectors")
Your point is well-taken, however, there are several kinds of camera collector.
Imagine a pile of leaves in your backyard - a collection, of sorts. Then imagine a bound book of stamps, neatly displayed, archived, protected, and cataloged. Another sort of collection.
One sort of camera collector is casual and uses the cameras they 'collect'. Another is a collector, completist, and archivist of the sort that would never sully a camera by actually putting film in it. I do not put these people down, I simply note that this is what they do - not unlike toy collectors who do not remove toys from the boxes, which would damage their 'collector value'.
The former sort are going to be less interested in film cameras when film is no longer available. The latter won't care at all. They are the sort who collect Roman spear tips, but they have no intention of impaling anyone.
Personally, I am of the former camp - I like to 'collect' cameras because it is fun, it is informative, it keeps me busy, it's cheap (these days) and I can take photos with many/most of my cameras. But it is a motley collection of this and that, some things broken and some badly in need of proper maintenance, but I don't care. When film is no longer readily available, there are a few I'll keep for sentimental reasons, but the most of them will be of no further interest to me.