Hello Julie. I am new to hamsters but on researching I have heard of so many hamsters who do not come out. I believe they can still be happy as long as they have food, water and enrichment. Hamsters are solitary animals so you need not worry he is lonely. I do not know if you are interested but I found this video about hamsters like this.
What is a Ghost Hamster? - YouTube
The person talks all about her experiences with such hamsters.