Even when you do have a open, staffed booking office it doesn't make much difference on a Friday or Saturday night (or anytime come to think of it!).
I have been told tickets aren't generally done on late night services leaving Manchester, as it just isn't worth the "trouble" over minor fares.
More important is to make sure all announcements are clear and loud, giving extra time at stations, with the time you "saved" by not doing tickets. Remember it is dark, and many people have consumed alcohol, may only catch the train going into town once a week, they need all the encouragement to get off at the *right* station!
I make sure a full ticket check is done before leaving the station, selling tickets before boarding, that way you can call on support from station staff/security/British Transport Police. It makes life a lot easier once you've left, you're on your own! (excepting Driver).
Our priorities are:
1) Safety of the train
2) Punctuality of the train
3) Revenue Duties (or as I call it, Collect & Protect)
It could have been something as simple as a broken machine, or even a flat battery, they could have hammered it on the tickets earlier, going into SHF! If this happens, I give an explanation on the PA, and walk up and down the train during the journey to give reassurance and ensure safety, rather than "sitting in the back".
If there wasn't "one sign of the guard" as you put it, who did the doors? Who made the PA announcements?