We had the opportunity to help my Great Uncle out with his second-story deck recently. We didn't manage to get a 'before' photo, but we did get some process shots. He only wanted to replace the wood that was in really bad shape, so we surgically removed half of the deck boards and wove new boards into the existing deck. I kind of like the two-tone result! But we'll let it all go gray to match and seal it next year.
The old boards were donated to a friend who planed them down and cut out the rot to build a deck in her own back yard.