I can see the reluctance to just waste the website (and it's current rankings).
Your options:
1. Have a competitor take it over, as is, and pay you for it. Problem is, they'll want to pay based on the profit they generate from the traffic the site gets. That's difficult to calculate and impossible for the vendor to track without detailed access to the buyer's accounts.
2. You could sell a 301. But that isn't great either. A 301 will result is the Google ranking disappearing pretty fast.
3. You could load the site with ads, affiliate program links etc. You'll lose the organic rankings in due course but you can make some money in the meanwhile.
The latter is what I did. For many years I owned highly competitive terms in SERPS.
This page of mine, for example, was #1 in SERPS for "make money online". For years! It made me £10K+ a month in Adsense alone. I had a completely
crap page for ERP software that was #1 for the term. Also "CRM software", "cheap laptops" and many more. For those who know what Adsense Fedex accounts were, I had multiple Fedex accounts. But I got bored, had other interests in life, and just ignored those sites, stopped updating, let them slide into oblivion. I don't know what the current rates of attrition are, but I suspect that if you do it properly you can make a few grand from affiliate programs etc before the site dies in the organic results.
What you do with the employee is completely open to negotiation and based on what he wants, the level of his ambition, his tolerance for taking on business risk and hassle ie setting up a Ltd company etc. If he's interested in taking this over why don't both of you go see this solicitor
together just to discuss options?