He seems fit enough and in good enough form to stay on for many years to come, but I think a lot will depend on his passion to keep playing. Also, he has a young daughter and I am sure his wife is definitely starting to get on his case about another kid and spending more time with his family...
The lucrative money that he could make in India, may also be a factor, when he could retire, spend time with and extend his family, and play a couple of months of cricket and earn millions...
What more is there left for him to achieve? He has done it all and I don't think he would really care about beating Tendulkar. Hey I hope he proves me wrong, but I don't think it will be form or records that determine his decision! And like so many other great players before him, he will retire well before the public thinks he is ready too!
As for captaincy, well it is hard to compare him to Steve Waugh and Allan Border, two of the greatest captains we have ever had! AB and SW were around in the "dark days" of Australian cricket during the 80's and have never forgotten! They knew never to take anything for granted and to fight until the bitter end! (Oh and tubby is in there somewhere too isnt he
) As for Ponting, he came into the game when Australia was at the top and helped them too stay there for many years to come, until recently he didn't know a lot about losing...
Anyway this has been an epic post already so I think I might stop there