If he is visa exempt, he can come to Canada with his expired PR card and see if they let him enter without reporting him for not meeting the requirements. If they don't report him, he can stay 2 full years and then renew. If they report him, he must appeal for his PR.
If he is not visa exempt, he can not fly without a travel document or valid PR card but if he can get or has a US visa, he could go to the US and enter Canada on the land border and try the above.
If he wants to apply for a travel document, the embassy will decide if he has mitigating circumstances for not meeting the res. requirements and decide if he keeps his PR or not.
If his wife has been living in Canada, she could sponsor him for PR again if he loses it. You would be able to sponsor him for a super visa if he loses his PR if you make enough money.