The PR card expiring doesn't mean that you are no longer PR. As long as your PR status was never officially renounced or revoked, you are still a PR and as such, you are allowed to live and work in Canada, register for health care etc.
However, as explained by Alurra, many govt. establishments have started to ask for a valid PR card as a proof of your status. Therefore, it is better to arrive in Canada with a still valid card in order to sign up for health care get a drivers license and apply for or re-activate your SIN before your PR card expires.