My PGWP expired on April 19th. But implied status gives me the right to continue working. I think the people who have said that they would mail incomplete application notice earlier are correct on this. Here's why I think that is the case:
Let's see Guide 5552 http://www.cic.gc.ca/english/information/applications/guides/5552ETOC.asp
We don't know what is considered incomplete but there could be clues, like on this line from that page:
All questions in this section must be answered or the application will be considered incomplete and will be returned.
Secondly, look at this page : Guide 5553 http://www.cic.gc.ca/english/information/applications/guides/5553ETOC.asp for extension as a worker
This line on that page says:
The Case Processing Centre will review your application to determine if it is complete. If your application is not signed, if all mandatory sections are not completed, or if the required fee is missing, your application will be returned to you and you will have to re-apply.
I think they do an upfront check for "completeness" before putting your file in that date's drawer or rack or whatever before they get to processing it.
I would still not suggest anyone to be as stupid as me and let their status be in an immigration limbo. When I first applied for it, I even thought I would make use of the PNP international student stream while this thing is in processing and hopefully before I get the BOWP processed, I would have something from Ontario. But then the OINP stream closed and I was left with no option other than LMIA, but let's not go there, for me it would have hardly done me any good. Given my financial situation and this limbo, I couldn't afford to stop working.