Just a thought...
If a list is falling back to Free from Premium... and might not like it, they may take 30 days to really discuss it, and 30 to act.
So maybe Archive their SubGroups etc, while allowing to see but no access, or perhaps as a teaser, no access but Read Only.
And SubGroups is my best example at this early pre-coffee hour. It might apply to other lost teatures.
Once these are "lost-forever," they may force themselves, in a foul mood, to live within Free. But if they can get them back within 60 or 90 days, voille. I had originally thought -30 days. But groups are ships and they turn slowly.