Without treading on the other thread, I'd like a discussion as to why comebacks rarely bring drivers back to where they were, sometimes very far away. There is the issue of being rusty, sure, but rookies do better than many returnees. Here are a few:
J Villeneuve 2004, 1 year away, he was 2 seconds off Alonso and that lack of pace carried into 2005 at Sauber, it wasn't until 2006 when he began to look remotely decent.
Alain Prost - 1 year off and was all over the place in 1993 compared to 1991.
Nigel Mansell - from demon in 1992, to slower than most number 2s in 1994, he got an unlikely pole in OZ but was slow throughout those 3 races and well into 1995.
Schumacher - Very unlike himself, although he got better the longer he stayed.
Mika Hakkinen - He was a serious contender for coming back in 2007 to partner Alonso. McLaren gave him a testing session in 2006, but was 3 seconds away from the pace and that was the end of that.
Kimi - hard to tell actually, how good he is in any given season is actually a bit of a mystery.
I hope Alonso doesn't take a sabbatical, the stats don't make such a move look promising.