Zos dont tell players much about their plans for the Crown store, so you won't get a definite answer. (Also I am writing this from memory so take it with a pinch of salt).

There is no reason to think that the black sench saber cat in the 500 crown starter pack will be removed soon. Starter packs (with different collectibles) used to be available just during "free play" weekends, so having this permanently in store makes the current version seem more permanent.

Will it change during the next freeplay weekend? Maybe, but the collectible changing seems just as likely as a discount on the extant pack.

P.s. if you prefer a black sench kitten to the saber cat kitten then today is your last chance as it was only available from the wild hunt crates.