Is there any chance of this happening? Almost certainly not. David Cameron's Euroscepticism continues to insulate him from right-wing dissent and keeps grass-roots Tories onside. Heseltine's prediction is a case of of the wish being father to the thought.
As I've noted before, the Conservatives' pro-European wing has been vanquished. It lacks the capacity to force a policy reversal. Cameron may well further alienate Angela Merkel and Nicolas Sarkozy, but given his emphasis on political consistency, he is unlikely to cite Keynes's dictum: "When the facts change, I change my mind. What do you do, sir?"
In fairness, it is doubtful that Heseltine himself believes Cameron will back down. It's far more likely that his intervention is designed to prompt Europhile dissent elsewhere in the party. In any case, such mischief-making proves that Hezza doesn't regard his position on Europe as a barrier to his return to government.