Contact an immigration attorney! Once you confirmed using Web Form after PPR that they are in Canada, they should not leave until eCOPR and PR card received. Web Form processing takes 3-4 weeks, there after P1, P2, takes weeks-months. People are waiting up to 2 months from P2 to eCOPR.... and then up to a month for PR card. So that could be easily at least 3 months at least before you get your eCOPR (could be sooner some times)
When the processed your Web Form or when the officer received an address update after the web form was processed, they verify with CBSA to confirm if your parents have an arrival record. Before they process this, if they receive information from CBSA that they have already departed - you have gotten your self in a very sticky situation as they will not be able to land them within Canada. If you did not notify them of their departure, that could be regarded misrepresentation - worst case this could lead to the file being closed/refusal
I have said this before as well: