My company recently really cut back on slack retention. At first I was frustrated, but we all quickly got over it and work carried on getting done at the same pace as before and nothing really got impacted like many of us imagined it might.
It's also not even really the same situation. A more apt analogy would be, if switching work laptops sometimes meant you could no longer read any Slack history.
Once communication with my customers moved to teams. I've had a very hard time to find historical agreements and decisions.
I try very hard to create a robust system for ADR logging now. And not just for system architecture. But for all decisions and agreements in my projects and across changes.