Not really. In a true DB plan the employer pays the cost of the ancillary death benefit, it does not reduce the normal retirement benefit. So there really isn't any "election" to be made. Why would employees opt out of a free (to them) benefit?
DC plans are different - the premium comes out of the account, so the participants pay the cost of the death benefit in a reduced retirement benefit. Here there is a valid choice to be made by participants.
Death benefits have to be non-discriminatory. If they are a function of the retirement benefits that are also non-discriminatory, all's well. So the death benefit (e.g. 100x the monthly benefit) is non-discriminatory in a DB providing non-discriminatory retirement benefits.
But now, suppose the DB plan is tiered - 415 max to owner, 0.5% benefit to NHCEs, then paired and tested with a DC plan for non-discrimination. The DB benefits are discriminatory on their own, that's why it's aggregated with the DC plan. So if a death benefit (100x for example) is provided in the DB plan only, the death benefit is also discriminatory. If the NHCEs death benefit that would be non-discriminatory is provided in the DC plan, that's a problem too because it reduces the projected retirement benefit in the DC plan. If the DB plan provides a death benefit that would be non-discriminatory based on some theoretical non-discriminatory retirement benefit that the DB plan doesn't actually provide, then the DB plan likely blows the incidental limitations.
CBs are typically a variation of this tiered DB. The CB benefits themselves would be discriminatory, so any death benefits that were just a function of the CB retirement benefits would also be discriminatory. If the CB is stand alone, then the death benefits would be non-discriminatory but again, the CB is a DB plan so the death benefit is employer-paid, so giving employees an opt-out for a free benefit is a non-starter.
Now there are lots of ways that some try to beat insurance into the plan using a "if it doesn't fit get a bigger hammer" approach. Some say giving ees the "option" for insurance in the DC plan works - I don't see how. Others figure out how much the death benefit needs to be in order to be non-discriminatory, then put it in the DC plan but also increase the ER contribution to the ees in the DC plan to cover the additional cost of the death benefit without reducing the retirement benefit needed to be non-discriminatory. In a theoretical sense this might work, but I can't imagine a TPA being able to make a profit on this unless they are getting a commission split. The fee-based market does not support the fees that would be necessary to adequately compensate us for this amount of brain trauma each year.
I imagine there are a few other approaches as well. For my own practice, retirement plans are complex enough as they are, I don't need to find ways to complicate them further, and I've never seen an rigorous economic analysis demonstrating the benefits of having life insurance in the plan. So I choose not to go here.