Why would you think the Greens have a future? The green philosophy has a future obviously but the Greens are too narrow on everything else to be considered as a prospect for government.
The NDP already own the Greens' prospective agenda, and they also at least partly own the environmental issues of the Greens. Not to suggest they aren't good people with the right views on the important environmental issues, but just to say their agenda is taken and they're treading water.
As an aside, issues over fossil fuels need a nuanced approach in the 21st. century and the Greens can't be that. That makes them too far ahead of the people of the privince.
You assume the Greens can't change and adapt like other parties. That may be a mistake. It is also clear that public opinion has been moving closer to the Greens on environmental issues, not away from them.