As far as the debate on captaincy is concerned, like I said before, there's no real point to changing captains in any format at this time, Dhoni should stay on as ODI captain whatever happens at the 2015 World Cup, unless he's retiring or doesn't want to captain anymore, 2017 Champions Trophy would be the best time for Dhoni to relinquish the ODI captaincy and maybe international cricket as a whole, gives the new ODI captain 2 years to get ready for the 2019 World Cup, which should be enough... Dhoni just last month turned 33 so he won't even be 34 when the World Cup comes around, from that point I'd say he still has 2 good years left in him.
Now the tour of Australia and the Tests, it's definitely our last away tour for sometime, I haven't checked the FTP, but the way BCCI have set up our scheduling, we basically play strings of away tours one after another with a home series with whoever's desperate for some TV money and is in a good relationship with the BCCI, that team seems to be the West Indies now, point being after the upcoming tour of Australia we won't see an away tour for another 2 or 3 years, especially not to South Africa, New Zealand, England and Australia, our historically tough away tours, so whether Dhoni wants to retire from Tests and in the process relinquish his captaincy or we sack him, it should be done after the tour of Australia, give whoever the new captain is a good couple of years of home Tests vs the very likes of South Africa, New Zealand, England and Australia to get his feet wet before we thrust him into the much tougher challenge of overseas Tests.