I don't understand the fuzz.
There was a schedule change and the OP lost the assigned seats.
So this is an issue of unassigned seats nothing else?
The OP still has a ticket and is booked in business.
Most of the times, this resolves itself as there will be seats available at check-in.
Or OP has to go to the gate and GA will call volunteers to give up their business seats.
If no volunteers show up OP will be re-booked (just like a revenue pax, aaward inventory is irrelevant in this case?) and compensated according to IDB policies.
Do pax on overbooked flights get automatically and involuntarily bumped to economy at check-in? I had never heard of this.