Twice before, the federal NDP has been in roughly the same position it holds now, emerging from an election with a relatively high historical seat count that was nonetheless disappointing due to the expectation that a seasoned and respected leader could have done better.
After the 1988 election, Ed Broadbent stepped aside as leader. And under a new leader in 1993, the NDP lost official party status - while watching the Liberals form a majority government and Reform take control of Canada's policy agenda.
After the 2008 election, Jack Layton stayed on as leader. And the result was the 2011 Orange Wave, which finally fulfilled (and indeed exceeded) Layton's hopes from the previous election.
Needless to say, it's not hard to see which of those precedents the NDP should be hoping to follow in the lead up to 2019.
And a similar pattern can be seen at the provincial level in the case of experienced leaders who have had to decide whether to stay on after disappointing results.
Allan Blakeney remained the Saskatchewan NDP's leader after being annihilated in 1982, won the popular vote in 1986 and positioned the party to form government in the ensuing election. (In contrast, Lorne Calvert's quick departure after his defeat in 2007 led to disaster in 2011.)
While Dave Barrett may not have returned to power after losing it in 1975, he was able to improve his party's position in 1979 and mostly hold those gains in 1983 - unlike Bob Skelly in the subsequent election.
Meanwhile, the only readily-apparent example of NDP meaningfully improving its position an election cycle after shedding a high-profile leader comes from Manitoba in 1981, when Howard Pawley was able to do better than Ed Schreyer had done four years earlier. But even in that case, Schreyer had stayed on as leader until being offered the position of Governor General.
Finally, the best-case scenario with a new leader might be that of Darrell Dexter - who didn't build much on Robert Chisholm's vote share in 2003, but eventually managed to build up support and win power in 2009.
To be clear, the above isn't to say that there's never a time to move on from a leader. But it's well worth keeping in mind that there can be a real cost to letting a single election's result dictate a party's future - and numerous precedents in which an experienced leader has had plenty more to offer after one disappointment.