And the NHLPA would actually do that?
For a limited time so that their players can get paid for the season while they negotiate the next CBA? Sure. There's no downside. They can strike next season if the negotiations are THAT bad, which isn't likely considering how close the sides realistically should be in comparison to other recent sports labor disputes.
I'm not talking about doing it forever. I'm talking about doing it to prevent the "strike at the playoffs" tactic.
And unions bargain away the right to strike all the time in certain instances. They ALWAYS have the right to strike for things like OSHA violations, but that's not an issue at all here. Bargaining away the right to strike for economic reasons is commonplace.