The answer from Downing Street is clear. Sort of. When asked 'Would he have to go?' No 10 insists on the same maxim. The Prime Minister is focused on winning September's referendum. The subtext is clear. Failure is not an option and is not even being considered.
In part this is the normal discourse of political campaigns. First Minister Alex Salmond always famously refused to answer questions based on negatives, such as "What will you do if you lose?"
Mr Salmond has always preferred to articulate his plans for when he won.
Indeed, no political leader likes to contemplate defeat, especially in cases, like the independence vote, when the stakes are so high.
But there are other reasons why Downing Street, and indeed much of Whitehall, is extremely wary of admitting the result could be anything other than a No vote. These include the effect such a statement would have on both the public and politicians across rest of the UK.
Questions such as who would control North Sea oil and what would happen to the UK's nuclear deterrent on the Clyde are only now starting to bubble through to voters south of the Border.
Some Tory MPs are also starting to wake up to the potential consequences of Scottish independence.
Some privately admit they believe that Scotland leaving the UK could be a boon for their party, helping it stay in power at Westminster, a claim contested by many on the Labour benches.
But others say they would be less pleased at the headache, and potentially billions of pounds of public money involved in, say, finding a new home for Trident. And so would many of their constituents.
The UK Government is also keen not to allow voters too many distractions over the next few weeks as it faces a tough challenge against Ukip in the European elections.
And, of course, depictions of David Cameron as a potential political loser are also always unhelpful - especially this close to a General Election.
But there are other reasons as well.
Any admission the UK Government could lose the vote would also increase calls for Whitehall to begin work on a potential divorce settlement between Scotland and the rest of the UK.
Already those demands exist. The Commons Defence Committee has said the Ministry of Defence should begin contingency planning for the event of Scottish independence. So far, the MoD has refused. Insiders argue it would be wrong to waste hours and manpower preparing for something unlikely to happen. Those efforts would be best directed at preventing a Yes vote, they add.
But calls for a Plan B are growing. As we get closer to the vote - and with the polls appearing to close - those voices could become even louder.
Not everyone in the UK Government sticks to Downing Street's carefully constructed position that failure is not even being considered.
Last week Defence Secretary Philip Hammond was asked if he thought David Cameron would have to go if he lost the independence referendum.
He could hardly have been more categorical in his answer. "I don't think that's an issue at all. This is not about the Prime Minister," he said.