Even if our budget had stayed the same or increased he would have left for a Premiership job. As he mentioned several times his ambition is to manage Chelsea and if a Premiership team came calling it's the next step on the ladder. I think any notions that we 'could have kept hold of him' are...
Gus said a lot of things, but when his stock was quite high and he had the opportunity to manage a Premiership team with a far bigger budget than ours he wasn't going to turn it down.
To be honest, although the board dealt with the situation pretty horrendously I get the impression Gus would have moved on to a Premiership team regardless.