Does that mean if a company goes under then there is no superannuation for its employees?
Again, I'm on shakey ground here but, that next to the last paragraph in the link Bob gave us indicates that the PBGC would be involved.
Pension Benefit Guaranty Corporation
If a defined benefit pension plan (traditional company retirement) is terminated because the employer has financial problems and cannot fund the plan, then the Pension Benefit Guaranty Corporation (PBGC), a government corporation formed under ERISA, will assume responsibility for the plan. The PBGC pays benefits after termination up to a certain maximum amount. Defined contribution plans (such as 401(k) plans) are not insured by PBGC.
Maybe somebody with more corporate bankruptcy knowledge will come along and shed more light on the particulars.