Oh Beth, I am so incredibly sorry for your loss of Mario!!!! I know what it is like to loose a dear pup so unexpectedly!!! Our hearts are with you and your husband!! I agree with Marianne regarding Luigi. I wanted to add that Luigi may experience some of the grieving symptoms such as wandering, not eating on a regular schedule and may appear just sad and not wanting to play at times. Yes surviving pets do grieve the loss of their companion too. You can talk to your vet about this.
You two be kind to yourself!!!!
Terry