At the time of my divorce I was granted one half of retirement benefits accrued from the date of June 20, 1989. I would like to know what happens if he passes away first? Can I recive the amount due me in one lump sum and if not who sends me the monthly payments due me?

Do you have a "qualified domestic relations order"? Has it been reviewed and approved by the plan?

If you don't know, you need to find out - ask your attorney.

If you do have a qualified domestic relations order that has been approved by the plan, the answer to your question should be in that order. If the answer is not in the order, or if it is not absolutely clear what will happen, or if you don't like what the order says, you need to get with your attorney pronto (certainly before your former spouse dies) and get everything cleared up.