A very considered reply and well put position, nice to see here!
I agree 100% about the client demand; that they don't really care about the underlying technology as long as their desired objective is delivered - however (and I fully accept that a may be wrong), I really don't think that Flash is going to be an acceptable technology to deliver, simply because of Adobe's recent announcement.
I firmly believe that in the not too distant future both workstation and laptop sales are going to be on fast decline. You may still have a workstation per household, you may even have more than one laptop, but I think that as the vast majority of what "normal" people do on a computer can now be achieved in a more aesthetically pleasing way on a tablet device, sales are going to reflect this (this is pretty much a 180 on the position I held a year ago!).
If (and it is an if) that becomes the case, we will be in a situation where developers will be forced to deliver clients expectations in a new way, be it feature rich browser experience or targeted app. I'd put my money on the tipping point being 2-3 years, not a decade, whether browser based technology is there or not!
iPad is the defacto market leader for tablets at moment, and according to the Gartner group, is likely to remain in that position well into the timeframe I estimate. If that alone wasn't enough, with no mobile flash support from Adobe, all tablets will present a potential problem. This means in order to balance the demands of likely audience with client expectation, we will be duty bound to recommend a solution which does not involve flash. To do otherwise would be selling them short - something akin to delivering a website that works only in Chrome.
I suppose to a certain extent the question was directed at developers who work exclusively in the flash environment. I know a few, but have no idea how common that is in the wider community. Those that have a wider skillbase already will I imagine be up to speed on the most acceptable html/js solutions, and perhaps looking at Android & IOS app development. Those that fit into the "flash only" department should I think be broadening their horizons while the existing work is still there.
Will Flash developers become app developers? Will there be a more narrow android developer vs IOS developer fragmentation? Is there even room in the market for flash developers with the existing developers? Will there simply be a more defined line between the role of front-end developer and back-end developer, which seems to have blurred somewhat in recent years? The future is certainly interesting if nothing else