maintaining RO is an individuals responsibility not a family one whether spouse is in Canada or not.
So whilst your wife as a PR would be allowed into the country if at the time of entry CBSA determine she has not met residency she could be reported which could eventually of course lead to PR being revoked. Having a valid in date PR card helps but always that risk and if having failed RO she would need to stay for 2 years without leaving to reset. It is just a matter of luck if reported or not, many people have no problems but no way to predict.
If at some point the PR card expires whilst out of the country still having not met RO then things get more complicated as she would need a PRTD if travelling by air. Just applying for one would highlight she at that time had not met residency possibly starting the process to revoke, again matter of luck based on circumstances at the time.