Why did he leave? If he has mitigating reasons for not being able to stay in Canada, he might be able to get a travel document. Mitigating reasons might be massive health problems in his immediate family where he had to act as a caretaker for a close relative or possibly but less so massive health problems of his own. Less so because he could have chosen to get medical help in Canada instead.
If he doesn't have mitigating reasons for his staying away, there is one chance that he has and that would involve not trying to get a PR travel document but instead get a visa for the US and enter Canada at the land border with his expired PR card. He will be allowed to enter and state his case and it would then be up to the immigration officer if they report him or not. If they choose not to report him, he could sit tight in Canada for 2 years straight without applying for anything at which time he meets the residency obligation again and can renew his PR card. If they report him, he can try appealing but if he doesn't have mitigating reasons for not meeting the RO, he will lose the appeal and lose his PR.
