We are headed into winter. Do you have active leaks? Is the condition so precarious that major damage to the house under the roof is probable? If so, you might have to put on a roof to protect the rest of the house. Your insurance company might deny your claim for water damage if the roof is that dilapidated.
Aside from the gamble on damage, a new roof will make your house more attractive than the competition that has an old roof, so you should be able to recoup, through the sale, most of the money you spend on replacing it. Even if you spend $10,000 to tear off the old roof and replace it..(always do a full tearoff. - my opinion. ) and only recoup two thirds of it in sales price, the action may be worth doing to get the quicker sale from a financed buyer.