If there are any days marked "as required" or "cover" on the rosters used for those drivers who work charter services, and there are diagrams with charter trains on them which need to be covered, presumably drivers could become available. That said I do not know how likely this is as I don't work in that particular part of the industry. I also don't know exactly what the proportions of ASLEF membership are for charter drivers in comparison to those for "franchised" (I use that term loosely!) passenger TOCs.
Aside from any actions seen as "breaking strikes", there are a few other items which would need to be considered which could make this idea unlikely to succeed. Unfortunately you have to factor in the potential anarchy when passengers heading for alternative routes, or queuing up for Thameslink trains, see a charter service and try to board it without heeding the conditions. You're looking at all sorts of shenanigans ranging from crowd control issues to non-payment of fares.
Then you have to consider the possibility of paths becoming available, especially if NR would be prepared to accept any sort of peak timetable from GTR up to 2200 the night before. 2200 is no time to be confirming to people whether or not a 1-train-per-day operation is going to be available for their commute. The paths required may also need special access to places like the [South] Eastern side of London Victoria, via Herne Hill or just the Chatham Lines (both of which would still see broadly similar levels of service as usual on a Southern ASLEF strike day) - there are not many other places you would terminate a special charter.
To give another example of what has to be considered, you have to work out the structure for booking, payment, customer care, dealing with replacement transport or refunds if the whole thing doesn't work, and more and more of the nitty gritty which comes with running a commercial passenger operation.
Although various elements of this will have been covered by existing charter operators and those booking charter trains in the past, for the most part these have been for ad-hoc leisure purposes, with little to no deliberate bearing on people's ability to commute to work at a time when the network (and particularly surrounding TOCs/other GTR brands) will be under incredibly severe pressure. Running a replacement for Southern therefore carries many risks and also will not cater for everyone, either with different travel plans or all those thousands usually carried from the affected area (Redhill/Reigate/Earlswood/Nutfield etc.) each day.
I would love this to happen in a way. I am not against the principle of running a replacement for a regular operator in disarray. I am local to the proposal and personally know some of the people who would benefit from this. If a more regular service could be run (say several trains, to cater a bit better for overcrowding or any charter cancellations) and it could be pathed efficiently, several days in advance, I would be much more positive. But it seems reality has bitten again, in one way or another, and I haven't heard much positive spin since the original idea hit the press.
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Is no one seeing the irony that the charter train will have to have a Guard?!
In a sense it's irony, but more like making a bit of a point as well!
Gaining a guard for these services would not be too hard. There are some who would work the Belmond British Pullman who I'm sure could be rostered, as well as any who sign the stock but could be given route conductors (I'm not sure Southern would look too kindly on it, but there would be a number of conductors on duty during the ASLEF strikes who could be hired and diagrammed to do it - plenty of different routes are signed, including some which are not immediately obvious!).
