If that does happen, Coventry depot will most likely become a WMR depot and lose the Northampton work. It would be easier to do that, than for the depot to lose all the WMR diagrams.
Therefore, Coventry will continue to work the Leamington & Nuneaton branches.
Or it’ll have one boring route card on LNWR if it does split
Leamington depot is the smallest LM depot I think?
I was wondering about that but there does not appear to be many pure Coventry-Birmingham runs so does Coventry also do the Walsall-Wolverhampton service? I have to admit that I don't know which depot handles the electric trains.
Leamington seems to be just an outstation for WMR as most daytime locals to Leamington are handled by Chiltern with WMR just dealing with the beginning and end of service. I remember that Leamington did not appear on the route map for the original franchisee Central Trains.
The OP indicated that LNWR would be operating the service but as the whole of the line falls within the remit of West Midlands Rail (the transport authority not West Midlands Railway the TOC brand name) then this line will be within the WMR franchise
I have read that West Midlands Rail wants the Birmingham Leicester service transferred back from the Cross Country franchise so perhaps we might be seeing this line used for through trains from Coventry to Leicester.
Really WMR need the stock to operate a much improved service on match days. One has only to see Cross City trains running through New Street when the Villa are playing at home or be at The Hawthornes when the Albion are playing to see the number of passengers that could be carried.