As Typescript is a kind of superset of Javascript, but tries to align with ES6 features, I'm always uncomfortable to count it as "another language than Javascript" I tried Dart, HaXe (for JS export) and Typescript ... and ended up coding in Typescript almost full time from December 2013 to fall 2014. It's such a pleasure to maintain big codebase. I take this opportunity to encourage anyone who never tried it before to give it a try! Last year it sounded like a gamble. Now that Google is also pointing into that direction, I think it's quite a good incentive to see it as something reliable with some future.
All that to say that IMHO, both JS and TypeScript (or a variant of it, like the defunct AtScript Google envisionned) will survive, because they share so much in common.