if someone applied for permenant residency and his study/work permit expired or will expire while he is waiting for CIC decision ,, can he/she stays in Canada under implied status till the decision is made or does he/she has to leave ??
I am pretty sure that only counts when you apply for another work/study visa. Not a permanent one.
In the best case scenario, you are implied as a visitor, not as a worker.
if someone applied for permenant residency and his study/work permit expired or will expire while he is waiting for CIC decision ,, can he/she stays in Canada under implied status till the decision is made or does he/she has to leave ??
This only works if you applied Inland with an open work permit application as well.
There is no Implied Status with Outland applications - you must maintain your status separately.
If you applied Outland or didn't include the OWP, you change your status to visitor (and apply for restoration of status if needed) or submit the OWP for your Inland application. Sometimes the OWP application and Spouse sponsorship don't meet up if they aren't mailed together, so I would recommend getting a visitor status asap for the time being. You can adjust your status as needed later.