Despite it being a gigantic wall, the addition of Alta Gateway will help the Gateway survive, but solely focusing on becoming a destination again, Gateway needs to serve as a neighborhood anchor. A place where people from around the Wasatch Front visit on occasion, say before Jazz games, and the occasional once, maybe twice a year visit from a family going to the Childrens Museum, or people visiting the Planetarium. I have preached this every since City Creek Center was announced, Gateway needs to cater to their neighborhood, their neighborhood being not only the Gateway District but downtown, N. Temple and Marmalade.
Megaplex is currently the only theater in Salt Lake City (the employees at Sugarhouse 10 weren't sure if it was going to change to first run, or if it was simply a major update but still discount movies), and with a major renovation will be that much better and will compete better with Century, in SSL. The addition of Game works will bring a few new people, but many burbanites won't simply choose Gateway on a regular basis, because aside from a couple of things, mostly museums, they can get everything else closer to home.
So yes the Gateway should continue to add new retail stores, and some entertainment options, such as a bowling alley, but differentiate the bowling alley and gear it to the downtown resident, and make it a once or twice a year type of attraction for burbanites, something along the lines of Jupiter Bowl in Kimball Junction, something upscale, not simply another all star lanes. Then work on getting a drug store, and a small grocery store, not a grocery store for all of peoples needs but a store that serves most peoples regular needs. Put those two new features in along with a new access to 500 W and that's a solid new northern half of The Gateway.