Speaking as one of those widows who now has to file single on a nest egg that was planned to support two of us, I can never decide what to do. We had no Roth money when DH died, and I have managed to get about $160k built up through conversions and after-tax 401k rollovers, but that's still only about 10% of my holdings. I'm at the very very very top of the 22% bracket, still working, but with a future of two pensions, starting survivor SS at 60 and my own at 70, and big RMDs if I don't do anything (and a strong belief that taxes will go up for me probably even before 2026), I feel like I should be converting to the top of 24%. Especially if maybe I want to buy a second home in a few years, since as of now about 85% of my stash is in pre-tax, and I'd get clobbered with a big tax bill.
No heirs, so that's not really even a consideration. I don't have any real objections to paying taxes, but would be aggravated if down the road I get some huge bills that I had known how to anticipate and mitigate but didn't bother.
If anyone feels like imagining what they'd do in this scenario, feel free to opine.