US Citizen Married to former Permanent resident living outside the US

I am a US citizen my husband is a Canadian citizen, he was a PR but gave up his status mid last year as we moved to Canada together. He did not have any income in the US in 2017, I had some. Should I still file as married filing jointly? Im sure since we were both living outside the US for over a year now we would be able to claim the income exclusion.

Should I file married jointly in the future as well even though he would then be a non resident alien? I'm unsure if the SSN he has/had expires.