Life insurance is NOT a 411(d)6 protected benefit; it can be eliminated.
However, in this merge situation, they can also elect to keep the pre-existing insurance and just not allow any more purchases.
So the first thing to confirm is that there is no desire to keep the existing insurance in the merged plan. Assuming that to be the case, then the contracts will be removed from the plan.
This can happen in several ways: First, the participants should be offered the option to BUY the insurance from the plan for the net cash surrender value. If they can't afford that payment, then the policies can be first "maximum loaned" by the plan so that a big chunk of the cash value is moved out of the contract and into the investment fund. Now, the contract can be offered to the participant to buy for a much lower cost (the remaining cash value, most likely less than 10% of the total cash value prior to the loan). Of course, the contract that is now transferred has the outstanding loan against it. Lastly, if the participant doesn't want to continue the contracts outside of the plan, then they should just be surrendered.