I have to get serious here... I have no experience or knowledge on the medical side of this, but personally, I would rather have the whole thing out than cut in half (ouch)... With some limited understanding of the anatomy of testicles, I don't see how they can take half. The top part is the epididimus (probably spelled wrong), and the lower part is the testicle gland itself. If there's something wrong with the remaining half, or if it stays sore for a long time, that would be a bad thing. I hope the idea of cutting it in half, isn't because your husband is trying to keep as much as possible, if the doctor has recommended otherwise. I know several friends who have had to lose one testicle for one reason or another, and they're just fine with one... No lack of hormones or anything.
What ever the case may be, I wish the best for him!
Charles