Biostar will probably be OK, because they are now the Asrock. Asrock built up into something big, now they only make the odd cheap board. That is where Biostar have come back into the market, but we don't really see them here (big in the USA though).
Foxconn have stopped, DFI stopped and etc. Gigabyte boards have been awful, not only corner cutting but also poor with voltage etc. So yeah, what with that and their recent horror show of GPUs I reckon they may go first. MSI have contracts with Alienware and god knows who else (I suspect Corsair, too) so they may hang in there. Either way I reckon they will still be making boards for Alienware etc. But yeah, Giga I am worried about. They seem to be making one cluster fudge after another and it is costing them.