It's definitely not dead. My best guess is that it simply lost the popularity contest to Medium. Svbtle's influence cannot be understated, however, in my opinion. I've seen a number of independent bloggers using their own "kudos circle" (inspired by the Svbtle feature)
I see why you think it might be dead, given that it stays quiet in the background and gets out of your way (as opposed to Medium for example), but that's the whole point of Svbtle.<p>Svbtle puts the <i>content</i> first - the content is the end game, where as Medium puts itself first; the Medium brand itself is put first; the content is just an afterthought.
I would say Svbtle had gone experimenting. At some point I decided I wanted to be a part of something livelier and more inclusive and announced in a review of Book Worm Lab <a href="http://ratedbystudents.com/services/bookwormlab" rel="nofollow">http://ratedbystudents.com/services/bookwormlab</a> Svbtle dead too. But now I'm using it again:)