From a mechanics perspective:
Make sure to put the tracking number manually into the case ASAP, it does not matter whether the tracking was already attached to the item, you will need to put it directly in the case as well.
The buyer will not win the case if you've attached the tracking number that shows delivered. (If tyou call it in they'll likely close it then and there in your favour).
From a customer service perspective:
It is entirely possible that the buyer did not receive the item, this has happened to me in the past where tracking shows delivered but buyer claims non-delivery.
In my case the buyer had already contacted Canada Post first. I contacted Canada Post and they provided the refund for non-delivery then and there I believe because they were already aware from the buyer's earlier contact.
With the very short timeframe around a case, you won't have received the $$ back from CP before the case closes. You might suggest to the buyer to contact CP in advance, it made things a LOT faster in my case.
I have not personally had to provide a refund after a case was closed in my favour but that's what you would want to do after the CP refund was received. If you can convince the buyer to close the case you can refund after CP pays (I'm assuming the full amount was insured). You'll have to be careful what option you choose for the refund, I think there is one for reason "item not received". Others may have more experience/suggestions about how to handle this aspect, or if you call in about it they may also have a suggestion as to how to refund without getting a defect out of it.
Make very sure to put the tracking number in the case ASAP.
