I beleive Bestwick and Cheever will still be calling this year's 500. I'd be surprised if Fox were interested. Early in the year their nascar and baseball schedule would be a tight fit. And if I'm not mistaken, they took the first part of the nascar season because once football starts in the summer they couldn't fit nascar in. So, I doubt they would want to try with IndyCar even if it is fewer races.
OTOH, NBC has the early part of the season more open until they pick up nascar in the summer. IndCar could be a good fit there. Or, heaven forbid, Indycar could cut a deal with some obscure cable company nobody gets like CART did years back with Spike TV. Ugh. But the Indy 500 being the crown jewel, I'm sure it will remain on OTA TV however they have to make it work.