It depends on how long you're staying in the house. If you intend to live there a long time, make the house work for you. You'll get much more value out of that than any notional loss you might eventually suffer during sale. But if you intend to move in the next 5 years, the best idea would be to talk with a real estate agent familiar with your market. They'll know what kind of hit you might take.

The last house I lived in had a mud room/laundry room/office area that was 12’ x 12’-

I took one look and said, I’m sold. Of course I loved the rest of the house even though it all needed updating. Everyone who ever came over was envious of that room. Three bedrooms is plenty, if you wanted to go from 3 to 2, I’d say no.

Is there any way to add to the laundry room without totally eliminating the bedroom?

Unfortunately, no.

Speaking just for myself, I would definitely do something like that. Three bedrooms is very common. I’d be surprised if it literally ruined the value of your home.

An easy way to get an idea is to look at current listings in your area. What are typical 3 and 4 bedroom homes going for?

Ask a local appraiser or real estate agent to do an appraisal with & without bedroom to know in confidence.

Usually when a house is listed marketed comparables CMAs are done to like homes in the nearby neighborhoods.

Could technically lose value when a room is lost,however it's not to say it will prevent it from selling to the right buyer for the same price. But be prepared to possibly lose some.