Rihanna wouldn't be affected by being too off the radar or being away for too long. Just like she isn't affected by over-saturation. The reason is because she, like Katy, is pretty inoffensive. Their reputation isn't so much that of an "exhibitionist" like a Bey or Gags or Nicki (or Miley now) so because of it they don't really polarize a lot of people. It seems that with Rihanna and Katy their success moves along one song at a time; if their single is catchy and radio likes it, they move up a spot. If it's not, they stall, and try again.
Sis...
Rihanna accepted an award from Anna Wintour dressed in a gown made of swarovski crystals this year.
She posed for a French nudie mag this year.
She got beat up on the way to the Grammys and then infamously went back to Chris a year later.
There are a lot of explanations for why Rihanna's reign won't let up, but "she is inoffensive" ain't one of them. ESPECIALLY if you're going to compare her to dull-as-dishwater Beyonce on that same metric.