I would dispute whether the cops we have would actually help in the situation you describe. Thanks to the Supreme Court, we already know that cops don't have a duty to intervene or save you during a crime. If anything, a cop being there might have caused the kid to pull the trigger sooner. The better way to prevent that kid from robbing you is ensuring he has a job available that provides him with better income and benefits than going around robbing people, and strengthening public unions is one small piece of doing that.

Back to the topic at hand, I think there is a middle ground available. I'd say public unions can only strike during contract negotiations and only after their current contract has expired. They shouldn't be able to strike mid-contract absent some very exigent circumstances.