If you are a PR, your SIN will remain the same. If you lost the card, you can go to Service Canada once you are back in Canada and say you lost your card and ask them to replace it.
For OHIP, you would have to go to OHIP and tell them the same thing, that you lost the card. They will give you a new one but if you were gone too long, you will need to live in Ontario for 3 months again before you get a new one.