Briefly, we have a holiday (flights and hotel) booked together with BA, for December. There are 5 of us going - it looks like one person won’t be able to come any more

we have paid the deposit, and the balance is due mid November.
my question is, can we remove this one person from the booking? The amount of hotel rooms will stay the same - so it’s just their flight we might need to cancel.
would we lose their deposit? (It was booked under the flexible covid guarantee)
Or would we have to pay for their whole flight, and claim back the taxes?
or would we lose their deposit?
im thinking if I’m lucky, I might be able to get their deposit back as a voucher, but I’m not sure if you can just cancel one person??
Thank you in advance.