Rewarding a large number of employees with unemployment was one of the stated goals of the company's restructuring plan (and had been warned up to a year ago - 9 plants iirc).
Tanking the company was not the stated goal, but the effective goal given the decisions made by the company over a number of years (not shedding debt at an earlier bankruptcy, taking on more debt when emerging from bankruptcy whilst also cutting wages and failing to start the planned, and essential for viability, infrastructure upgrades).
Ie the company's ultimate demise was the foreseeable end-game anyway; it just happened "now".
Which means that a potential buyout of viable product lines and infrastructure will happen sooner - providing jobs with a mgmt. profile (likely Bimbo Bakeries or Flowers) that isn't so clueless. Or, these competitors will (without product line buyout) increase sales to fill the hole left by Hostess - still more jobs.
I don't know how, given the Hostess recent history, the whole blame can be laid at the feet of the Union/s.
Whatever their responsibility in this, it is a shared responsibility, and is dwarfed by other factors -- and many of these factors were the mgmt.'s to control.
* I should add: our son works for a privately owned NE US grocery store chain. They didn't carry Hostess - in fact in the industry they were known to be unreliable for some time now.