I would say so in my personal opinion. I have knows guys in my work (Transport related) to contest a speeding fine and they usually end up getting humped by the courts
What do you think the chances are to losing his licence then, practically 100%?
It all depends on the factors i.e Age, road/ weather conditions etc. At the end of the day he is sadly guilty so contesting it would only take up more of the courts time and usually this gets their backs up. If its his first time offensive then he should be ok. Pleading guilty will make the decision much easier for the court and also the court will see that he is aware of his offensive so hopefully this will be enough for him to obey the speed limits especially in roadwork. Lots of ganger's are killed each year while working on road surfacing etc so he will need to remember this when making his plea. Sadly ignorance is not tolerated by the courts so its best to man up and plead guilty as he definitely won't get off with it whatever he pleads.
Yeah it is his first time offence and it was dark etc etc, regardless like you said just best to plead guilty and take what happened like a man rather than getting on the courts nerves.