1. Even if you don't get reported, you have to live for at least a year with an expired PR card. This will give you problems if you try use it as an ID or somehow get involved with IRCC.
The fact that a PR card has expired has NO impact, none whatsoever, on a PR's status.
An expired PR card should not cause any problems in transactions with IRCC. They can and will easily verify a PR's status. As others have said, there is no requirement to have a currently valid PR card . . . and NOT even for entering Canada. A PR has a statutory right, which the law considers a "privilege," to enter Canada, no need for any particular document, just sufficient proof to establish identity and status, and either a CoPR or an expired PR card in conjunction with a passport is sufficient for this, and indeed just a passport establishing identity will work but might involve some time waiting in Secondary for CBSA to verify status. (A valid PR card will probably make border crossing easier, but it is NOT required.)
A valid PR card is mostly needed to obtain permission to board a flight headed to Canada from abroad.
Technically the PR card is not supposed to be "ID," but as I recall some provincial offices will consider it as such.
Well, the law might not explicitly say so but your expired PR card can also get denied as being invalid.
Depends on what the PR is using it for. Some provinces will recognize an expired PR card as valid proof of STATUS. I forget the time period, but Ontario, for example, explicitly recognizes expired PR cards as proof of status when renewing a health card or drivers license, for up to three years as I recall. (That said, I have never been asked for proof of status when renewing either, and it was only after I last renewed my OHIP card that I noticed they still have me listed as a Permanent Resident even though I have been a citizen for more than five years. I will try to remember to get it changed the next time.)