You don't understand what I'm trying to say. The process of how a roster gets worked out is not "We have time for exactly (I'll use a random number here) 30 characters.", it's more a "We have time to make around 30 characters, let's see how many we can put in."
The final roster could be any number around 30, and characters are added or scrapped based on how interesting/fun their gameplay is, or how significant they are to the game (e.g. Mario, Ryu or Jin Kazama would never get cut from any game of their respective series).
This is how fighting game rosters get developed. Aside from the must-have characters, there's no "slots", only an approximation of how many more characters they can put in with the remaining development time, if they even do that. If Ike (for example now) gets scrapped during development, that doesn't mean that immediately after, another character will take his "spot". Heck, even if he gets scrapped in the initial roster draft, it doesn't mean that another character will take his "spot". It's more likely we will end up with a game with 29 characters instead, because scrapping a character's development usually is not done because the developers think the character isn't "worthy".
What I'm saying: There's no exact number that they're clinging onto and absolutely have to fill. After all, if Ike gets scrapped, who says they are going to use that additional development time to make a new character? What if instead, they put more time into making another stage, another couple of items, whatever?