Should David Shearer’s South Sudan appointment be confirmed, a byelection is likely in Mt Albert, signalling the departure of the last ex-Labour leader and leaving the question hanging: did the party err in knifing him?

“Former leaders” are a mixed blessing for a political party – they can be weathered, wise old owls, or they can be ghosts of parties past; or they can be just a bit bloody bored. Just a few months ago, the New Zealand Labour Party was full of the species: if you happened to be a member of their caucus you had a one in eight chance of being either a former or current leader of the party.

Then Phil Goff began the longest striptease in political history, culminating in victory in the Auckland mayoral election. David Cunliffe announced he would return to the private sector after the 2017 election. And this morning (just another quiet news day in a quiet news year) it emerged that David Shearer is, almost certainly, on his bike, too: leaving – to regurgitate this morning’s most overused joke – the Labour Party for the relative sanctuary of war-torn South Sudan. This is no cushy gig or clever National ploy to jettison a foe, however; rumours have abounded all year that Shearer was looking for a Labour exit plan involving the UN, but challenges don’t come much steeper that South Sudan, and Shearer’s pre-parliamentary CV shows he’s qualified.

While his appointment as head of the United Nations mission is yet to be confirmed, Shearer will leave a hole in the Labour Party in the foreign affairs shadow portfolio – he bore a genuine authority in the role, and on issues such as the refugee crisis and Australia’s offshore detention system, he delivered thoughtfulness, passion and gravitas. On his day, he was among Labour’s best performers in the house.

He had visibly become disgruntled, however, if not at times embittered. On issues such as the TPP, for example, the centrist and trade advocate was palpably becoming aghast with the direction of his own party – and he wasn’t granted the get-out-of-whipping-free card that fellow TPP-cheerleader Goff enjoyed.

For Shearer, the big what-if will always relate to his resignation from the leadership in the middle of 2013. Following wave after wave of destabilisation, much of it emanating from caucus colleagues riven by infighting, his departure became inevitable, punctuated with the whiffy closing quotation marks of two snapper held aloft in the house of representatives.

Shearer’s advocates point out that neither of those who came next, David Cunliffe or Andrew Little, showed in the polls that they could do any better. Shearer was never given the opportunity to lead his party into an election. Could he really have done worse than the Cunliffe-helmed effort in 2014?

Certainly, he had a scratchy start, and stumbled routinely in media appearances, but he had only been in parliament since 2009, when he succeeded Helen Clark. It sometimes seemed as if he was cursed by being cast as Labour’s answer to John Key, and the energies of his backers in trying to sculpt him into the form of a modern, relaxed leader suffocated him, made it harder to develop his own style. It can be a struggle to be yourself when surrounded by a group of people shouting BE YOURSELF, LIKE THIS at the top of their lungs.

When he left the role he was still relatively new to politics, however, still relatively new to leadership. And his performance at the 2012 Party Conference, in a strong speech that included the launch of the KiwiBuild policy, showed he had the cojones.

But it could be that, for the Labour Party, the most important leader since Helen Clark is in fact John Key: as the Labour Party scrambled hopelessly to work out how to take him on – go for the antithesis or try to ape him; attack him as wolf or as a flake? – the leaders were knobbled from the start.

In that regard, Andrew Little may be the luckiest of the lot – not only has the universe cleared out the haunted corridors of leaders past, it’s now relocating easily the finest New Zealand politician of the generation, John Key, to Hawaii. If Little fucks it up next year, he has no one else to blame.

Meanwhile – unless the next prime minister calls an early 2017 election, a byelection is very likely in Mt Albert (another of those seats, like Mt Roskill, in which National in 2014 won the party vote). Every MP for Mt Albert since 1981 has also become the leader of the Labour Party. And Jacinda Ardern moved to a house in the electorate earlier this year.