As others have already said, Maverick will almost certainly be okay to return home. When people are new to stomas & surgery they are often overly apprehensive about what 'might' happen. However, this is usually a passing phase and with more experience they come to understand that many of the things they worried about simply don't happen.
A five year old golden retriever should be well past the the boisterous puppy-stage and would be less likely to jump on him ( unless he encourages it to do so). They are usually very easy to train and are the preferred breed for guide dogs and service dogs of all kinds. I would proffer that there will be a service dog group somewhere near that would be only too pleased to give advice on how to train Maverick if that becomes necessary.
We are looking after a boisterous young retriever at present whilst my daughter gallivants off to Glastonbury. He has a tendency to want to be physically close and (at first) would think nothing of walking all over us! However, it only took a few moments of 'training' to stop him from putting his paws anywhere near the stoma. He now gently sits next to me and rests his head on my knee, rather than clambering over us. There is little doubt that such dogs can be much more benefit than they might be a nuisance and the sooner your friend starts on the road back to 'normality' the better he will feel.
I wish you and him well for a happy reunion and ongoing companionship.