I think Democrats will do what FDR DeFacto did, threaten to pack the Supreme Court if it rules against Democratic legislation or if it strikes down previously settled law.
Obviously if the 6-3 Republican Supreme Court strikes down the ACA or overturns Roe V Wade, the public favorability of packing the Supreme Court will likely increase significantly.
So, I expect the Democrats will take a 'wait and see' approach on that, much as Joe Biden de facto did in the debate.
They won't have to wait for long in the case for ACA. If SCOTUS strikes it down we may reach the point of no return for both the filibuster and court packing.