If you have a firm buyer who is offering more than the buyout+tax and you can come up with the cash, buyout the lease and then sell the car. If I am not mistaken, someone is on the hook for the remaining payments. And if you return the lease, you are on the hook for excess mileage and excess wear and tear.
Here is a Nissan link to information about lease buy-out.
https://www.nissanfinance.com/nmachelp/ ... %20charges
You should get a quote
By the way, if I am understanding correctly, a person who wants to buy your car could not buy it directly from Nissan. *You* have to buy it, and then sell it. I'm not sure how trust issues would be dealt with if you are buying out the lease with someone else's money but I'd like to hear reasonable approaches. I may be interested if these issues can be sorted.
Where are you located ?