I am sorry for your loss. That is really hard.
Remember that the essay is a chance for the AO to see who you are as a person and to think “This would be a great person to have in our community!” So yes, you are right in wanting to make sure your essay isn’t “sad”.
Focusing your essay on something you did/learned from your dad and how you carry that in your life is a great way to show your resilience and what matters to you.