That’s a question for your vet. Is this fur loss due to the dermatitis? What was the trigger for the dermatitis?

I’m with Petzy.
I would definetly schedule a appointment to have your bunny looked at by the Vet. I think if he has lost that much hair I would stay away from the creme till the vet makes sure it isn’t the culperate and a allergy or something.
How does the skin on the tail look?

I doubt he’d get put to sleep just due to some fur loss. It’s better to take him in to get checked out. You can always say ‘No.’ if they say to put him down.

Absolutely. You are the decision maker for his care and treatment, and you always have the right to refuse a kind of care, including euthenizing, suggested by a vet. However, by deciding not to call the vet to describe the change and ask if he should be seen, you are making a different kind of medical decision that may not be in his best interest and lead to more drastic needs later. You can call, tell the vet what has happened and how it’s progressing. She will know if a side effect of the treatment is more hair loss, or whether that indicates a different underlying condition that needs different treatment. I’m glad it’s growing back, but please don’t self-diagnosis. Bunnies have a much stranger anatomies than we imagine and we really can’t know what’s wrong without an expert. Even dog/cat vets often don’t feel expert in rabbits!

Sounds like Obbie is in good hands so far, so trust this vet to help in the next step. Their LAST choice usually is to put him down. Don’t be afraid.
{{{{{{{{{Healing vibes, Obbie}}}}}}}}}

The tail’s skin color depends on his pigmentation. If the fur on his tail is white, or partially white, pink will be the expected color of the skin there.
I love the name ‘Obbie’ — so cute! But I wonder if he had or has a parasite that is responsible for the dermatitis. If yes, the vet should examine him to make sure Obbie is rid of it now or to prescribe a treatment..