Newcastle are not planning on holding him and are already looking for replacement as it stands now, and I would be high regards for Newcastle if they can respect his decision to leave especially looking how other teams have treated their star players when they decided to leave for a bigger opportunity.
That's clearly not what the fans felt, though. Respect goes both ways to begin with. I'm not sure which story is true, but some rumors suggest that Newcastle promised a pay rise but failed to do so, hence why he wants a move now. The fact that the club failed to sign players probably contributed to that, although those aren't good reasons to act selfishly from the fans' pov. Whatever the result of this saga is, Newcastle needs better management to help it navigate the market for the future. They can't let their top targets move to other clubs easily again.
Newcastle fans needs to understand that a player of his profile ought to be playing in a higher competition winning better trophies but the pay rise may have kept him since he never hinted before that he wants to move out of the club.
I hope this won't make the fans hate him but rather come to an understanding of everything with time which may be difficult. Anyway, if no deal fall through i hope he stays and give his all again for another season before moving out.