My parents did not meet RO when they returned in 2013. I believe that they had ~ 1 year stay (less that 2 years RO requirement) when they had to leave Canada. They could not continue staying for RO and apply for PR (wait for a year and then get PR renewed) as they had to leave to take care of my uncle just before PR expired.
We are Canadian citizens and as we had to be back in our home country for my assignment. As we were not in Canada, they could not apply for PR TD (after my uncle expired). In fact, we renewed our Canadian passports while we were in home country. We returned last year after my assignment was over.
In addition, since my brother (who is also a Canadian citizen) went to our home country around that time. As he was there, my parents were okay to be there even though they are 78-80 years old). However my brother will now be returning to Canada in July 2018 and now our parents need to come back permanently to stay with US as we are only brothers.
FYI - they cannot come to US cross the border and they have to take flight to come to Canada.
Thanks in advance for your advice....