"Unlikely" is a huge overstatement. If the Supreme Court strikes down the entirety of HERA, it would be an unprecedented action by them, especially in light of the fact that the Fifth Circuit already did sever a part of HERA even though it lacks a severability clause.
I don't think this is impossible, just so unlikely that it isn't worth considering.
Also, keep in mind that the Supreme Court striking down all of HERA does not in any way mean that current shareholders would have to benefit. Calabria said that FnF shareholders should have been wiped out in 2008; such a ruling by the Supreme Court carries the risk that all current FnF shareholders get zero.