Yeah, Lisa...any time we lose someone who played an important part of our holiday celebrations, there will be a period of adjustment. I was lucky enough to have both set of my grandparents live until after I was married. We always spent the holidays traveling to their houses. After they passed, our holidays became drastically different.
One of the best ways we can honor their memories is to be thankful for the time we had with them and share that with those we love. I pray that you can utilize the opportunity to do that this holiday season and look back fondly on the holidays you were able to share with your mother. It might even be special to sit down with an audio or video recorder and talk about those memories with your dad. You'll be glad you have those later.