How the payoff actually works at closing
The lawyer handling the sale pays the outstanding mortgage balance directly from the sale proceeds before anything comes to you — this is routine and doesn't require the lender's advance permission for an ordinary sale.
Why speed matters more here than in a typical sale
A lender that isn't being paid can eventually start power of sale proceedings, which shifts control of the process and timeline toward the lender rather than you. Selling before that stage starts keeps you in control of the price and the buyer.
What if the house is worth less than what's owed
If the mortgage balance exceeds what the house will sell for, that's a shortfall that needs a conversation with the lender and likely a real estate lawyer before listing — it changes the math but doesn't automatically stop a sale from happening.