I strongly recommend some to cover the unknown-unknowns.
First, you guys are in good shape. If you could survive forever on one salary, then you don't *need* anything. But wouldn't you want the survivor to be able to FIRE on schedule instead of now living paycheck-to-paycheck, or having to cut back a ton to get back on track?
To my mind, though, the bigger issue is flexibility and lack of worry. The reality is that you can't possibly know how the survivor will feel, what s/he will want to do, or how the financial landscape will change. Maybe the survivor will want to continue working full-time, which might push your expenses up if you now need the flexibility of a nanny. Or maybe the survivor will want to take 6 months off, or drop down to part-time for years, to manage the grief and kids and probate and all of that, so now you need income replacement. Or maybe the survivor wants to move back to family for the extra support, which requires moving expenses and maybe a salary cut or higher living costs or whatever.
The point is, you cannot know what the survivor is going to want to do -- but you want the survivor to be able to make all of those kinds of decisions over time, without any worry about paying the bills or feeling like they have to jump into major lifestyle changes. Dealing with the death of a spouse/parent is almost inconceivably hard, and it totally fucks with your ability to make logical, rational decisions. And it's hard to describe that until it happens; believe me, I've seen my extremely competent, frugal, FI mother go into a complete tailspin and become incapable of even managing a decision tree when her husband died. I am not exaggerating. This woman runs her own business, is worth several million dollars, has been FI for several decades, makes a ton of money, has very low expenses, always handled the finances, etc.; I swear, she is the poster child for financial competence. And yet a month after he died, she was sobbing at my table that she didn't know how she was going to get by without his income, had to ask me to call the pension company to figure out what she needed to do to get the payments started, needed me to go to SS with her to set that up, etc. It was shocking. Really and truly, the rational part of your brain is just overwhelmed with all those panic hormones, and logic goes out the window. And that's when bad decisions get made. Heck, the woman who my mom bought her house from back in the '70s had just lost her husband and thought she couldn't afford to keep the house, and then when she came to her senses regretted that choice for decades.
So. If you want to minimize the risk that the survivor does something life-alteringly stupid, do whatever you can to minimize any immediate financial pressures so they feel like they can at least afford to wait a year or two before making any big changes.