Savitar is certainly powerful enough to be able to return Jack's memories, but he's even worse than the Doctor when it comes to being pedantic about what he can/can't or should/shouldn't do. There would have to be a damned good reason for him to act on it, and Savitar does not think like most.

I can imagine Jack going to extraordinary lengths to protect a child, given the lingering guilt he feels over Gray.

As for Artemis, you are right, she is going to be very sorry...