My tech blog at https://grepular.com/blog/ has about 1100 feed subscribers. About 1000 of them are Google Reader users. I'd be really interested to see what would happen if Google dropped the Reader service. I wonder how many of those people would resubscribe from elsewhere.
Nice feature of GReader is that it uses browser native engine with all user mods - adblock, flashblock, greasemonkey, stylish etc. Stand-alones that I've used are mostly Trident (IE engine) so despite their great features they are also annoying.
So for your question - it will take lots of effort to relocate RSS reader and large portion of user base will be lost in transition.
The scary thing is how Reader seems to have been so suceessful that it has become almost the de facto RSS reader. After Bloglines went offline it has become the only usable web-based mainstream feed reader. Reeder, the best feed reader on the desktop, even relies on Reader for the feeds. If Google decides to kill it or -- God forbid -- integrate it into G+, then RSS maybe threatened. I'm hoping some new player will show to disrupt RSS, because it's needed to fix Google's virtual monopoly.