If Obamacare in its entirety was tossed by the USSC then the Democrats would be able to claim they had done their best to help the common man, only to be thwarted by the "conservative" leaning USSC. They also wouldn't have any political risk when Obamacare measures kicked in and killed the job market.
I think what will happen instead is that the mandate will get thrown out, but the rest will remain with nothing to pay for it. This will be really bad for Democrats. They will lose a critical revenue stream for the bill with no way to make it up. The cost of the program will explode along with the corresponding federal deficits.
We will all be hosed, but the Dems will have a tough time shedding the blame.
If the mandate is struck down, Obamacare will collapse like a house of cards. It will be unsustainable.