You appear to have described a 'Category 3' offence because 'harm' is clearly low (as a broken collar bone is a relatively minor injury within what GBH can cover) and 'culpability' is also low (because it wasn't, for example, a sustained attack or an attack where the victim has deliberately been hunted down in order to attack them).
While a Category 3 GBH offence can result in a custodial sentence, it would be very unusual as the 'starting point' that a judge must use is 'high level' Community Order and it would take something like a repeated offence (and a not guilty plea to it as well) to see custody considered.
So you husband will almost certainly receive a Community Order (i.e. unpaid work).
See pages 7 to 10 here to read exactly what the judge must refer to when considering sentence:
http://www.sentencingcouncil.org.uk/wp-content/uploads/Assault_definitive_guideline_-_Crown_Court.pdf