Justin Trudeau is not responsible for making sure the NDP keeps their base. Nor do I think he's the reason they're losing support. They went from a party that was pro-worker party to one that is increasingly out of touch with the working class. Building a party full of college activists comes at a price.
The working class is also drifting to the right. This is a fairly universal phenomenon. Not something that is just the fault of Trudeau. We see it in the US, in France right now, in the UK during Brexit (although the UK is swinging away now). This is largely the failure of neoliberalism hitting home. Trade policies that shipped jobs elsewhere and immigration policies that brought their middle and working class here to suppress wages and jack up real estate. Backlash is understandable.
Maybe. But you still haven't made a case for how it's in the NDP's interest to pull the trigger right now.