Retaining residency while living outside canada after getting passports

[liz9000]

Hi All
I need an advice from my senior members.
One of my close friends (married couple) lived in Canada till 2007 and got their passports. As they got passports, they got job in UK and have been living there since 2007.
They have not applied any tax returns since 2007.
Are there any factors that can affect their residency?
Are they liable to spend any time living in Canada in five years or ten years in order to secure their residency?

[steaky]

What passport? If they are leaving Canada after being tax resident, they need to file a tax return.  Generally, if they are already Canadian citizen, they don't need to meet PR residency obligation.

[liz9000]

Yes, they have Canadian Passports.
They have been out of canada since 2007 and have not submitted tax returns.
Shall they be submitting tax returns with zero value as they have not generated any income in Canada
Or they need to declare earnings what they had in UK