It is not up to IRCC or CBSA. If a sponsor withdraws at any point before the PA lands, the app is cancelled. There was a case a few years ago where the sponsor withdrew while the PA was on the plane coming to land in Canada.Your wife can withdraw her sponsorship at anytime up until you land. If she withdraws before the application is approved, then it will be cancelled. If the application is approved, she can ask to cancel it up to the time you land, but it’s up to IRCC or CBSA to decide if they are going to do that.