They can absolutely sell. The first 250k (500k if married) of *profit* is excluded completely from taxes. And then any profits after that are taxed at 0%, 15%, or 20%. If you're making that much money on a sale you're not getting my sympathy that you might pay < 20% of your PROFITS. Get out of here with the pity for the well-off.
If they don't need the cash bad enough to sell, then don't sell. If they do, they'll have quite a nest egg after.
If they don't need the cash bad enough to sell, then don't sell. If they do, they'll have quite a nest egg after.