It wouldn't happen anyway. They didn't keep May just because she was the R/S girl. Once the 5th gen starts rolling, Hikari will be an outdated "last gen" girl as well, so she'll obviously get the boot if the anime continues.
I do wonder if Marina showed up at the start of G/S if she would have been part of the group instead of Misty. Sure, there was nothing for Marina to do back then, but Misty might have left at the end of Orange if Marina was invented at the start of G/S. It would have probably been better that way, since Johto only ruined Misty's good reputation and made her personality as interesting as a wooden plank.
Funnily enough, there are still whiners on Bulbagarden about this. One guy was shocked to hear me say that the reason AG was liked more than Johto because it had May instead of Misty. Hello? Do you have a head on your shoulders?
(For those of you that don't want to read another one of my rants, you can skip what I say below....hey, at least I'm warning you guys this time.
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Aside from AG being better written, the writers pretty much banked on May to revive the show for them. This idiot couldn't get it through his thick skull that introducing a second protagonist and the Contest arc (which were brand new at the time), were more exciting than Misty and her boring Togepi.
Amazingly enough, these are the same people praising Hikari despite the fact that she doesn't bring anything new to the series.
Why did a completely original character like May get bashing despite her replacing dead weight and actually having a plot, yet Hikari get praise despite her just being May "Round 2?"
I really feel sorry for those people. Those bitter fanboys honestly believed getting rid of Misty was a bad decision, and would have prefered the already stale Kanto trio to go on for all of Hoenn as well. Do these people know what good writing is or would they have prefered to run the show into the ground just because of their Pokeshipping and Misty?
It's amazing that May is the most bashed female character in the anime simply because she replaced Misty. You will never find as much people hating May as much as they do the other two girls, and not that she warrented any of it, it's simply because Pokeshipping and Misty had to go down the drain forever because of her. These are the same people who like to "pretend" that Hoenn sucked now and praise D/P, just further examples of their cowardice.