Looks like you're taking the right tack with things. Make sure he does have a will done, if somehow that's not something he has. A living will as well I believe, which is something all of us, even us young'uns need(ask somebody in the healthcare industry if they have a DNR, and why). Since he doesn't need the assets, whenever you do get around to investing the 850k, you can take a bit riskier of an allocation, no need for something like 70% bonds/30% equity, somewhere between 50/50 to 70/30 equitys/bonds, or something like the Wellington Fund(Vanguard), or a mixture of strategies.
I don't think he'd benefit from robo-advisors, but I could be totally wrong on that. The benefits that I can think of mostly revolve around tax treatments and such.
Somebody else might have more advanced strategies for converting the IRA money into Roth and cash, which something something, might be better for you and any other siblings on the back end of things.
It looks like he's in great shape financially though, and you're asking the right questions!