How can I protect my hardwood floors without sanding and refinishing?
You could apply a few coats of a water-based clear finish to the floor. This you can apply with a roller and it dries fast so you can probably do two or three coats in as many days. Then later, if you choose to to a more complete job, you will fix the sag and then re-sand the entire floor and apply finish again. This would only cost you the price of the can of finish and a paint roller.