Yeah no-one will be able to replace warne from our current stock of spinners. But then again, i guess you gotta understand that Warnie was one of a kind, maybe even once or twice in a century for a single country who revolutionised the standards and expectations for leg spin bowlers. Same story with Gilchrist was a wicket keeper batsman and Murali as an off spin bowler.
From our current stock of spinners, there isn't really that much depth now i think about it. Cullen has 87 first class wickets at an average of 42.49, Cam White has 131 first class wickets at 38.38, and i think there's a newcomer called Daniel Doran who's got 23 wickets at 29.73. The plus side to the last 2 spinners though is that they can bat quite a bit (Cam white has a first class average of 35ish with the bat, Doran averages about 26ish with the bat and Cullen is decent for a tailender, giving about 15 runs per wicket in first class cricket).
When McGrath goes, at least we'll have a decent amount of talent going around to try and fill the gap (Lee, Clark, maybe even Dizzy will stay on...Johnson and Tait look the goods as far as young talent goes).