I feel like this sums up my current situation. I spent a few years learning Unity and developing a tool kit that I was really happy with, only to have the web plugin killed and the crap-tacular WebGL exporter be the alternative. After a few months of HTML5 engines and all the frustrations of cross-browser support and canvas/rendering/audio/scaling quirks, I switched to haxeflixel.com for it's Flash support. It does have a html5 exporter and I find that when it works it works great, but if you get any errors post-compile you really want a pure-js engine like Phaser to debug.
I feel like I'm stuck between a rock and a hard place right now. Use Flash and risk it all going up in smoke in under a year? Or move to HTML5 and just hope it gets better and not worse over the next few years, putting up with all it's annoyances and quirks?
That's software engineering, though. Platforms rise and fall for reasons completely unrelated to your efforts. Languages come and go. New markets and verticals emerge, and your bosses insist that the entire company has to pivot because Twitter Cards are totally the next thing! In fact, that's life…
The savvy response is not to stew and fume over the demise of your favored target. Sigh, brush off some books/docs and get to cracking on whatever is next.
What I do not understand is why so many of you seem fixated on browser-based delivery. Have you looked around recently? People love the idea that they have their time-wasters and toys in their pockets, accessible at a moment's notice. Gotta wait until your number is called at the DMV? Whip out your phone. Waiting for your doctor/dentist? Whip out your phone. Riding the subway/tram/trolley/bus/street car/Uber to work/date night/wherever? Whip out your phone.
What I'm saying is that you should be making mobile apps. And, let me be clear: the economics of mobile apps are a shit show, but games are about the only vertical that is consistently profitable, even without excessive use of in-app purchases.
So. If you're just making games as a hobby, and you don't care if anyone else plays them, then who gives a fuck what tool you use to make it? Build it in Flash, and take on the responsibility of ensuring that you always have a stable Flash plugin for your hobby hacking. But if you want to make games as a social effort, even if not (yet) a business—if you want people to discover, play, talk about and recommend them—then you need to go where the people are. And that sure as shit ain't Flash in 2015.