SpongeBob's been on TV for more years than both of those two Disney shows combined, and I doubt either of those two Disney shows reached even close to the level of popularity that SpongeBob's gained. Canceling SpongeBob now would be a much bigger thing than canceling Mickey Mouse Clubhouse and Jake and the Neverland Pirates.
"Bad Seeds" and Pig Goat Banana Cricket, if I'm not mistaken, are at least two of the cartoons still planned to come on Nick, anyway.
Nick does want to make sure it has plenty of live action, but that, also, doesn't automatically suggest it's going to get rid of all the Nicktoons soon. I assume SpongeBob's airing less partially to increase the diversity in the schedule and partially to give more value to SpongeBob having his presence in the upcoming movie.