Well Zayn's girlfriend is apparently the reason for his decision, so I guess she is yoko uno in all of thisI can actually see a Beatlesque thing happening now with 1D. When John Lennon left, that was it for the band.
I know circumstances are completely different but I'm not sure how the remaining band members are going to carry on with Zayn gone. The dynamics of the group won't be the same obviously. Who knows?