Lool a watch will never replace a phone. Being able to type on whatsapp, watching tv shows and movies on long commutes, these are things a watch will never be able to replace.
The day i get an Apple Watch is when its battery life is at least a week long and it will only server as a quick glance notification device and gps tool if I'm walking an needing directions.
It can replace being my music player for when im in the gym cause I would rather that then a phone in the pocket. But for what i mentioned earlier a watch can't replace those things.