Don't know about the US. In Germany, it's covered by the unemployment insurance (if the employees have been employed for at least 12 months prior to the unemployment -- otherwise it's covered by unemployment money II aka basic safeguard ( = welfare ), if the person is eligible ).
In the US, you have welfare and food stamps, right? This can give people time to find a new employment.
If a company announces bankruptcy early enough, people can start looking for new jobs in time.
It rarely happens that a strike causes a bankruptcy. Normally, both side should negotiate terms of employment acceptable to both employer and employees. In Germany, we have a system that invokes a mediator in such cases, and agreements are usually reached before damage gets too large for the company.
Small companies with less than 20 employees do not have "union contracts" in Germany. Because they do not have a company council that represents the rights of the employees, only larger companies have that.
Also, we do not have unions in several branches of economy.
In small companies, employees have only limited rights ... and the government punishes when people quit their jobs (cuts or even loss of unemployment money claims), so most people are trying to keep the jobs they have or if not, try to accept any employment offer.
In larger companies, the company council has to agree when people are laid off.
I'm not sure about regulations in the US.