Not a hypothetical: Hostess folded, as did Yellow trucking. Unions can’t save a business from bad business decisions or destructive market forces.
But businesses fold all the time, union or no union. When business is good, unions make sure the employees get a fair piece of that.
To an extent, this is already happening. I work in manufacturing, and the last couple of years there was more demand for our product than our factories were physically capable of producing, and prices were raised to weed out the number of customer orders to what we could handle. Projections for this year are for softened demand, and sales expects to have to offer significant price cuts to keep enough orders for our manufacturing lines to stay busy.
Collective “we have enough stuff and will buy less” at work.