Tom Albanese's justification for scrapping Rio Tinto's tie-up with Chinalco was that the world changed. The chief executive was right: Rio's London shares were up about 38 per cent between the deal's announcement in February's pit of despair and the point of walking away in June.

But since replacing that deal with a planned iron ore production joint venture with BHP Billiton – along with a mega rights issue – the shares are up another 44 per cent. The price of protecting Rio's five-year debt from default, which more than halved while it toyed with Chinalco, has fallen another 70 per cent. Should Rio turn tail again?

Rhetoric on both sides suggests the venture is very much on; they aim to produce a binding agreement within three weeks. But if resolve were weakening in the Rio camp, it would be entirely understandable. With leverage shrinking and capital spending rising – including in the Pilbara – pooling its highest-growth, highest-returning assets with BHP's inferior portfolio does not seem as smart as it did five months ago.

All along, Rio's stated priority has been to cover the $20bn Alcan debt due this year and next: the $15.2bn from the rights issue, asset sales of $4bn, and another $4.5bn from selling bonds and axing the interim dividend has given Rio ample headroom – without any “equalisation payments” from BHP.

With at least $10bn of synergies to be carved up between the two, shareholders – about two-thirds of whom own both stocks – would need some convincing to allow the JV to lapse. But BHP could raise earnings per share next year by a tenth simply by buying back shares, on Citi estimates.

As for Rio, a second U-turn would be curtains for Mr Albanese. But for the sake of consistency, if nothing else, he should be setting aside a few hundred million for yet another break fee.