When is the status of a deceased retirement plan participant determined, after retirement or after death ?

My uncle technically retired from his job as single on March 5, 2009 with no designated beneficiary in his retirement plan. He married on March 10, 2009, but he died on March 15, 2009. What status should be followed in his retirement plan in order to determine the beneficiary?
This is an Employees Retirement Plan
I mean company pension.
Not Union pension, but company pension.
There is no best answer nor right answer here.

If he designated no beneficiary and he had not added his wife to his retirement plan, the funds revert to the retirement plan administrators and are used for future retirees. Was this a union pension, company pension?