I dont think bitcoin will kill off all other ALT coins. Imagine 5 or 10 years from now end users are selling their products online and accept multiple forms of payment BTC, ETH, LTE, etc. Why not??? Just look at this chart here.
Anyone can just create an alt, there will always be alt coins but they are testing ground for bitcoin. All alts are priced in bitcoin and they do take some value away from bitcoin but nothing we can do thats the beauty of crypto.