A) Judging by the resistance to change displayed by some on this forum, some of whom I assume must be photography pros, there will be some people who will remain skeptical of smaller, lighter, newer gear. In other words, change is hard and a lot of people are fearful of it.
Resistance to change should not be confused with preference, or not drinking the Kool Aid. I don't think anyone is fearful. The "change" you talk about is not a big change at all. Mirrorless has been around for a long, long time. I doubt anyone is fearful. Smaller, lighter gear? You are referring to the camera bodies, obviously. Even then, you are not referring to a Canon high end MILC body. None have yet hit the market. Lens wise, smaller and lighter is not currently the case by any stretch of the imagination.
B) DSLRs just feel like more solid gear, even though this is actually not the case (more moving parts, etc.). But they are generally rugged and heavy and do have a reassuring feel for those that use them. Better ergonomics for those with large hands, etc. (no Trump jokes, please).
Are you sure about less moving parts? IBIS requires moving parts. How many compared to a mirror box? I have to wonder how rugged those little parts (IBIS parts) are in the camera if dropped. Also, more moving parts does not necessarily = less rugged. Example: Sony's weather sealing problems. There are thousands of products on the market right now that have thousands more moving parts than their predecessors, and are far more rugged and reliable than earlier products. Example: Cars, airplanes, etc.
C) Perhaps there will be a resurgence (much as there is for 35mm film SLRs these days) and people will start buying used DSLRs on eBay as a novelty. These won't be pros, but could be one reason they hang around.
Won't be pros? Now how do you know that? Anecdotally, I personally know one pro who seeks out old manual lenses and uses them in his fashion work. The worse the lens the better, for him. He's currently seeking a Praktica film camera to add to his tool box. He shoots digital and film. Film cameras are not a novelty to him.