You can pretty much bet it will all be about the money and any compromises will be glossed over. The recession/depression caused by Covid will leave the UK coffers dry and dropping a no-deal Brexit on top will just add to the pain.
The current contract was based on a 'no less service' than that which the military provided and memories are short so don't be surprised if some erosion od standards occurs for the sake of lowering the cost.
As for aircraft types, you would need an honest appraisal from the CG concerning the S92 - how often has that big lift capability been used and how often has that big downwash been an issue? If the 189 is as good as claimed and can do 95% (or more) of the S92s jobs then perhaps a mix of 189 and 169 might be the option.