Almost certainly more DOO as a compromise saving
DOO doesn't just save you the guards' wages. It also means that any on board staff have more time to do revenue duties, and that you can also get rid of dispatchers because with cameras you can see the whole train even on a curve. You do need to have something in place to deal with assistance, but that doesn't require nearly as many staff, and if you have an OBS they can do it.
With respect to all guards (particularly one very good one who posts here), if it's a choice between closing routes and destaffing, it's destaffing for me every time. Let's not make the mistakes Beeching made in this regard, basically seeing the only two options as "full service" and "nothing", and not considering "railway, but staffed as a bus would be" as a middle ground.
On the other hand it is booking offices I would look at first. This Wiki article:
https://en.wikipedia.org/wiki/United_Kingdom_railway_station_categories shows how many of each we have - there are presently 1320 stations which have some form of staffing. The full list is here:
https://webarchive.nationalarchives...ger/stations/betterrailstations/pdf/partd.pdf
It would strike me that all of 679 "Category D" stations should be destaffed as a priority, with most "Category C" stations to follow (but perhaps not quite all; it might for instance be worth retaining some "end of line" stations like Ormskirk and "touristy" ones like Windermere with staff). All "Category A" and "Category B" stations would remain staffed. This would probably mean maybe 100-150 stations retaining staffed booking offices, probably in some cases with reduced shifts. That's more than I originally thought, but could save a lot of money by destaffing about 1,170 stations without having any impact on the actual passenger service. Other than Merseyrail, almost all of these stations already have TVMs, so no added cost there. To avoid disadvantaging passengers, e-tickets would be enabled for all flows nationally without exception, ideally including PlusBus if Ticketer could be persuaded to update their scanners to scan e-ticket barcodes.