Here's link to an article that shows rendering & plans for the Hard Rock on the Las Vegas strip -- the former Mirage. The article is 18 months old, but seems to cover the changes as I've heard them described.

The main body of the Mirage hotel (3-wing hotel, etc.) remains mostly intact. The added Guitar high-rise hotel will be built where the volcano now sits. The Guitar wing will have some slots & table games, but most of the gambling floor will stay where it currently is, beneath the 3-wing hotel.

I'm sure there will be a complete re-theming to the Hard Rock look.

See:
https://www.casino.org/news/hard-rock-shares-new-renderings-of-guitar-shaped-las-vegas-hotel/