Selling a big house at/near the bottom of the market to move to a smaller one in a worse location or living mortgage free is a difficult one.
The cost of moving is not cheap and will living in a smaller house work for him especially if the location is not as nice ?
If it were me i would look at the mortgage on the current home to see if it can be made cheaper, possibly convert from capital repayment to interest only for a while till things get easier, assuming he's not interest only already. If he's on a high fixed rate is it worth him paying any penalties to get a cheaper interest rate or if on a variable rate can he get a cheaper deal (some lenders SVR's are still above 4% where as some new tracker deals are below 2% dependent on circumstances)
Can he make other savings in his life style to make things easier for him, he's gone without holidays but has he got sky, gym memberships etc that could be cancelled.
If he's happy where he lives then it should be worth the sacrifice but its a very difficult one to call.