Residency Appeals
As mentioned in the section on Permanent Residents, to maintain your PR status, you must be physically present in Canada for 730 days out of every five year period after you become a Permanent Resident. You can refer to that section for possible scenarios that enable you to rack up days as a PR even while you're outside of the country.

If for whatever reason, CIC decides that you have not lived up to your residency obligations, you will have the opportunity to challenge that decision before the IAD. There, the IAD will take into consideration humanitarian and compassionate considerations, as well as the best interests of the child, in making their decision. If you are outside of Canada when you are informed that your PR status is at risk, you will have to request to be allowed to enter Canada to attend your hearing.

Issues surrounding PR status are very complex and for that reason, the assistance of a lawyer is probably advisable. There are also numerous ways of retaining your PR status while overseas, but the nuances are subtle. A brief consultation with a lawyer can give you piece of mind about not being in the country.