To specifically answer the question WWYD.
I would not get a dog I didn't want, that would almost certainly be entirely my responsibility in terms of care, training and that I don't want to pay to insure, feed and pay vets bills for.
I wouldn't want to bring a creature into my home, that would be 100% dependent on me when I already had a raft of other responsibilities .
If I were not a dog person, don't know anything about them from even the most basic thing i.e. how long do they live, and not having a dog had been a red line for me I would not get a dog.
I'd be researching the actual needs of the dog and how it would impact on my family, homelife, working life.
I'd be researching what the exact benefits of a therapy dog would be for my son, how that would work and if those benefits outweighed the negatives on the family as a whole.
I would be asking myself if I could love a dog and do all I needed for it for the entire duration of its life, for 10 or more years out of my own life.
I'd be wondering how I could schedule in all the care and two good walks a day for the dog.
I'd be considering if my son likes dogs and does he have any fears/allergies etc that might make this a problem.
I would be wondering why my OH had done this without speaking to me.
I would be wondering how he had come about this dog as his story is incredible. I'd be thinking had he got some stolen dog off of man in a pub, and was bringing home a whole lot of trouble for me.