Again, it's all speculation. Bolding "are invalid as a matter of law" doesn't make the point stronger. Language is important, and if you read the entire paragraph you posted, Disney is only arguing to the invalidity of the notices, which subsequently makes the Thomas Brothers claim premature. They are not arguing that the Thomas Brothers no longer have a claim to Predator because of it.
" There now exists between the parties an actual and justiciable controversy concerning the validity of Notice One and 20th Century's and defendants' respective rights. Defendants' notices fail to comply with these statutory requirements and are invalid as a matter of law. 20th Century seeks a declaration pursuant to 28 U.S.C. § 2201 that defendants' notices of termination are invalid. This action is necessary because defendants are improperly attempting to prematurely terminate 20th Century's rights to the Hunters Screenplay, at the very time that 20th Century is investing substantial time, money, and effort in developing another installment in its successful Predator franchise."
Would Disney want the rights of Predator exclusively? Of course. Can they cancel the Thomas Brothers claim forever because, while apparently timely, there was an error or errors in the filing? I don't know. Neither do you. But all we have is the information that's been provided to us, and the information provided to us in Disney's counter-claim is not indicating that the Thomas Brothers claim is no longer invalid, it's not, but rather just premature.