Only your friend can determine what's "worth" it to him. But, the key is to have every part of the "deal" worked out at the time it's done.
1. How much of a voucher.
2. Hotel (which one)
3. Meals
4. What's the reroute look like? Is it in F, is it a good seat, will it involve flying into the Midwest/East Coast where there are storm cancellations/delays already posting?