Here is the thing, the NDP and Greens will have to face the electorate at some point in the future no later than May 11, 2021 (sooner if the government falls or they could change the fixed election act to five years but that would be political suicide but May 9, 2022 is the absolute latest by constitution they can stay on) so voters will get to pass judgement and if they felt it was a bad choice they can punish them.  We don't under the Westminster system directly elect a premier, we elect 87 MLAs and they determine who can command the confidence of the house.  Technically any resident of BC who is a Canadian citizen over 18 could become premier if the majority of MLAs back them even if they were not a leader of any party.