If he died before retirement his benefits will be what they are. If additional contributions could be paid now these would get 40% tax relief if they were paid to his pension rather than hers. As it's unlikely a final salary option is available for the extra contributions they will go to DC.
That is still leaving her dependent on someone else's goodwill. Given his behaviour that is a rather large risk
In a DC scheme yes the trustees decide how to allocate the funds on death. DH could nominate Battersea dogs home or his OW. Yes the trustees could pay to either of these but no set of trustees are going to do this if he has a financially interdependent wife which OP is
If they did it could be challenged with the Pensions Ombudsman and they would have to justify as why they made such a perverse decision
They may split the payments so the wife gets a proportion of the benefits. That proportion may not be enough for her to live on. The ombudsman overruling a nomination completely would set an interesting precedent for anybody to challenge. We have had many people furious that the children of the deceased are getting a share instead of solely the second wife who was the only one on the nomination, especially when it goes into trust with the ex as a trustee.
If he dies in retirement it will depend on what is selected but the market for annuities has dropped through the floor since pension freedoms were introduced as the rates are appalling. And if he spends the household income by frittering it away why is that any different to what he could be doing now? Does he need to be retired to fritter?
Yes, the market is rather crap, it was crap before the legislation was introduced and seems to be getting worse. He doesn't need to be retired to fritter, but he is earning and making pension contributions now, they have spare money and the ability to make more by continuing to work. Being retired and frittering is rather risky, he could easily withdraw all of his funds into his own private account and spend it on a Maserati, leaving them both in an uncomfortable situation. That will not provide either with an income and again OP would be screwed.
If they split up and his pension is final salary she only has to transfer if the financial agreement is that the pension is shared (it could be offset against other assets) and if the scheme is not underfunded and reducing transfer values. And actually it will only not provide "anywhere near the amount it would in a DB scheme" if she does not obtain an actuarial report which takes into account the differential between the two types of scheme
If offset against other assets that doesn't resolve her retirement income issue, she would need those assets to set up home again. Many DB schemes do not allow the ex spouse to keep the fund with them, they are required to transfer out and usually the only option is into a DC scheme which will not provide any guarantee on income or fund growth which would leave her financially ruined.
For me the risk would be in retirement that the wrong options are selected but this might be outweighed by the extra tax relief now that the DH would get, allowing them to build up additional savings not in pension form
Assuming the DH doesn't decide to leave her and then refuse to divorce for a while, or he hires an excellent solicitor which OP would not be able to afford on her wages.
So all the pearl clutching about her need for a pension by several posters seems over dramatic to me
I don't think it's overly dramatic. It isn't the most important part of financial planning but it is significant. I have not yet met an IFA who thinks having a pension is optional. OP needs to make financial provisions to take care of herself, depending on someone else to take care of you financially for your entire lifetime is far too risky, her DH should want her to be making pension contributions to maximise the chance that she will be well provided for. If they're still together then this will benefit him as well.