If he loses in Burnaby, he HAS to stand down. immediately. Losing in Burnaby would guarantee that there was no possibility of the NDP avoiding catastrophic losses with Singh as leader, possibly 1993-style catastrophic losses-and it took decades to recover from that.
The man has made no impression. It looks as though he doesn't WANT to make an impression. Yes, he won the leadership, but he's done nothing with it. And the NDP, the only progressive major party in Canadian politics now, is now in a fight for survival.
It Singh loses in the byelection, there is no case for him staying on as leader. There is no HOPE for the party if he stays on after losing Burnaby.
It really is that simple.