The first step that the Crown Prosecution Service has to use when determining an assault charge (and a court subsequently has to use when determining whether it's the correct charge) is to examine the extent of the injuries sustained by the victim. With the injuries you've described, there would seem to be no doubt that 'GBH' (rather than, say, 'ABH') is appropriate.
Then, with a GBH charge, the CPS (and court) need to decide if 'with intent to do some grievous bodily harm' should be added to the charge. It's ultimately up to a court to decide whether or not 'intent' was present but the CPS has provided guidance here
http://www.cps.gov.uk/legal/l_to_o/offences_against_the_person/#a16
and my view (based upon your account of the events) is that 'with intent' is most certainly justified.
With luck your husband's offence might be seen as Category 3,which means that the minimum sentence that can be passed will be one of 3 years imprisonment minus a third for an early guilty plea = 2 years. Offenders are normally released at the halfway point in their sentence, so he'd actually serve 1 year in prison. (That's assuming the minimum sentence being passed; 4 years less a third might be more realistic, so that's 2 years 8 months, meaning 1 year 4 months actually 'inside').
However it's possible that (through hitting someone who was unconscious) 'culpability' might be seen as 'high', making it a Category 2 offence. If so, the minimum sentence that could be passed would be one of 5 years less a third = 3 years 4 months, meaning 1 year 8 months actually spent in prison. (Again, a slightly higher sentence, of 6 years minus a third, might be more likely. So that would actually mean 2 ywears in prison)
So it looks like your husband will spend between 1 and 2 years actually 'banged up', plus the same amount of time on licence (when he'd have to report to probation officers and be barred from things like foreign travel, plus being at risk of immediate return to prison if he fell foul of the law again during that period).
You ask whether the case will go to trial. That could only happen if he pleaded 'not guilty' (which would appear to be madness as it would simply increase his sentence). His first court appearance will be in the magistrates court, where the case will automatically be referred to the Crown Court. There might be one or two procedural hearings, followed by a sentencing hearing.