Funny, and here I thought it felt like it was already gone.
I uninstalled Flash from my previous MacBook Air and iMac two years ago, and haven’t installed it on my new Retina MacBook Pro. Besides a couple of stubburn websites (which have been incrasingly thwarted by changing Safari’s browser agent to iOS) and the occasional tiny feature at a big site (like one particularly obscure Facebook photo upload dialog that I haven’t had to use in a long time), I haven’t had a reason to miss it that entire time.

