Gmail is very far away from extinguishing open email, because that's such a huge target, but it certainly managed to make a dent. How many users have forever left the open ecosystem of smtp/imap/pop tools and service providers because of Gmail's growth? If Gmail hypothetically reached the market share necessary to mortally wound that open ecosystem, do we have any doubt that it would eventually do it?
And remember, email is the largest open ecosystem in my list. Where is the fully open alternative to iOS? Answer: it doesn't exist because Android captured all the momentum from the emerging community, and channeled it into a platform that is now closed for all practical purposes. In this case, extinction has already happened.