Do we all agree that a ban on pre-existing condition exclusion without individual mandate would bankrupt the insurance companies? It's like allowing you to buy car accident insurance after the car is totaled.

So if individual mandate is ruled unconstitutional, then HI companies need to hope and pray that pre-existing conditions ban, a very popular item, never gets put in place. Otherwise it's sudden death

To have it done by a conservative USSC would have such a sweet irony to it, that I am tempted to give money to these legal efforts.
No, we don't all agree. That conclusion is based on a number of unsustainable factual assumptions.
This bill, with mandate, is predicted to cover about 32 million people. Of those, about 15 million will come in under the Medicaid expansion, with the rest going into private insurance. Of those, about 3 million are estimated to be currently uninsurable due to pre-existing conditions. That means the other ~14 million are people without pre-existing conditions. Your argument is based on the assumption that if the mandate gets kicked by the SCOTUS, the insurance companies will be forced to take on 3 million sick people and get no new healthy customers to make up for it.
The first problem with that assumption is that striking the mandate doesn't strike the subsidy, which on average pays for about 2/3's of the premium costs. That is obviously a significant inducement for people to purchase insurance, with or without a mandate. Somehow I think if the federal government suddenly started saying they'd pay for 2/3's of the cost of BMW's, BMW sales might just skyrocket, no?
Let's conservatively assume, for the sake of argument, that with no mandate, only 5 million of those 14 million are induced by the subsidies to buy insurance. That means the insurance companies have to take on 3 million sick people, who they can charge 150% of the standard premium costs, and 5 million non-sick people. It's probably not a good deal for the insurance companies. Collectively, they may lose some money on that.
However, insurance companies are currently doing very well off the employer-based large and small group markets. Mandate or no, those markets will continue to be their largest and most profitable markets. So even if the insurance companies lose some money in the individual market as a result of the bill minus its mandate, somehow I think they'll muddle through off the profits of their existing market which will likely be 90%+ of their revenue stream, and I doubt they'll lose terribly much in the individual market since the subsidies will induce enough healthy people to buy insurance.
Killing the mandate will weaken the cost containment strategy of the bill to some degree. It won't, however, kill off the insurance industry or force government subsidies to keep it afloat.
- wolf