I'm offering a slightly different perspective here: he may like the feeling of having money in bricks and mortar - many older people love the psychological security of this - especially if he is sufficiently clued in to be concerned about negative interest rates in the bank. That is a real concern, as is inflation. He sounds like he's in good health and so could live for another 10 or so years....can he afford to sell and have money depreciating in the bank?
The best-case scenario if he keeps the property is that the refurbishment work will be carried out quickly and without much hassle and that a good and reliable agent finds a good and reliable tenant, allowing him to put off the decision to sell for another while and hopefully increasing the re-sale value of his property. This could work out very well and often does, despite the scare-stories we're all familiar with. We all know what the worst-case scenario looks like with rental properties, as a landlord I'm all too aware of what can go wrong, but it seems to me that keeping the property for now is a real option to be considered and I wouldn't dismiss it out of hand.
Does he have an accountant to file his annual return and keep on top of the tax side of things, LPT payment etc.?
If he's feeling a bit vulnerable and has had a tough time with lockdown isolation it might not be a good time for him to make the big decision to sell the house. He could regret it, especially if he faces a big CGT bill and is worried about his money rotting in the bank.
He sounds like someone I helped recently in a very similar situation - an elderly and extremely independent man who lived alone and managed all his own affairs privately until his health suddenly broke down. It's very hard for someone like that to let people in and to give up control so I would tread very softly and respectfully no matter what you decide to do. If he does put off the decision I would encourage him to revisit it and make plans when he's feeling stronger, it's much worse when ill-health forces a total loss of control over one's affairs. Best of luck.