The reason I asked is, unaccompanied instruments can be miked somewhat more closely, because you only need to consider the balance between direct sound and reverberance. But the addition of a keyboard instrument creates several problems.
Number one is the balance between them in terms of clarity. For a baroque 'cello, the keyboard instrument would most likely be a harpsichord (or less likely, a clavichord) and the range of size and projection among different harpsichords is considerable. But there is a miking distance in reverberant halls beyond which the sound of any harpsichord degenerates into mostly noise. And depending on the lid position, you may have only a limited range of elevations to choose from.
I would definitely want to record (or at the very least, listen to) a rehearsal in the hall, and have a definite idea of the physical setup of the players, before deciding on the mike setup for the concert. Is that an option for you? If not, then can you at least talk to the players and make some napkin sketches to get an idea of where your mikes could go?
Also, what's the hall like, in terms of its sonic character?