I'm sure I'll be in the minority here, but I would have no ill feeling towards him if he backflips. The reason why; he'd be absolutely stupid to turn it down.
He's not even officially started here, and let's say he does now have the option of South's, his choices are;
1 - Honour his word to Leeds, move him and his family to other side of the world, changing schools, leaving friends, worse climate and standard of living etc etc to coach in the vastly inferior SL competition, carrying out a pretty tough rebuild job, at a club where winning comps as become expected, but the squad needs a major overhaul
2 - Stay in Sydney, with zero change to family circumstances, to coach a team where he already works, with some of the best players in the world, who are a genuine challenger for the NRL title.
Head coaching gigs in the NRL will not come available that often to a relatively rookie coach, certainly not at clubs the size and stature of South's.
It's absolutely in his best interests, he has to do what's best for him and his family, and I very much doubt anyone else would choose option 1 if they're really honest.