I think Missy is a poor example cause endorsement dollars leaving Phelps are going to go to her at some level. She'll likely take his spot on Subway commercials.
People like Nathan Adrian, Matt Grevers, Rebecca Soni, and Dana Vollmer, who have won multiple gold medals, still are definitely are going back to being anonymous after the Olympics are over and will only get money from the likes of Speedo, TYR, and Arena.
Vollmer has a shot at a certain level of stardom for at least a few months because she's quite pretty. I had no clue she won a gold back in 2004 though. No one knows who these people are.
I had never heard of Missy Franklin until a handful of days ago but I imagine she'll stay quite well known due to her age and success. Unfortunately for Allison Schmitt, she has no real future at receiving recognition due to her poor looks and goofy voice. Using her would be a marketing nightmare.