It is your responsibility to renew your PR card. Do it. If you get citizenship soon, CIC will refund the cost of your PR card. I think it's only $50 or $100, so best to do it to be safe, right?
An expired PR card does not mean you no longer have PR status. PR are not required to have a PR card. COPR document should be enough to establish status.
There is no requirement to have a PR card in order to apply for citizenship. Citizenship officer/judge is supposed to accept COPR as proof of PR status unless there is an active investigation of your status by immigration collegaues they are made aware of.
Thank you everyone for your answers ! I hope to get the invitation letter soon, to become citizen and be able to travel some where warmer. Good luck to everyone.
Good luck - its hard to tell how long it will take to the oath without having some more detail on your application as this will indicate if there is a risk of a post test RQ. It all depends on if you want to spend 50 bucks on a new PR Card or not really.