Yes, severance is like every other obligation, different only probably in seniority.
Obviously if the company is bankrupt they cannot pay.
Don't work for companies that are going, or could be going bankrupt. In the vast majority of the cases the writing is on the wall long before that happens.
Payroll taxes are just another form of income tax, the company doesn't really pay it, the employee does, economically speaking that money would go to the employee were those payroll taxes not to exist. The the co. does pay it is just an accounting issue.
