Keep former group members in the transaction history
When a old group member is settled up and removed, his name becomes "[removed]" in the transaction history. It'd be useful to still have his name for record-keeping.

I could see how this would be helpful for tracking expenses down the road. I’ll talk to my teammates and see if they can fit it into our schedule.
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Pallab De commented
A derivative of this:- Provide the option to deactivate members.
For example: My two of my room mates have moved out, but one of them is continuing with me. I want to be able to deactivate them so that they're not included in Splits by default, without deleting them and the previous transactions. Currently, the best solution appears to be creating a new group. However, the ability to deactivate members will provide more flexibility.