#3 Relinquish the title and move to the main roster
Asuka was ready to graduate to the main roster months ago, so at any given moment, if she made an appearance on Raw or SmackDown, it's doubtful anybody would bat an eye in confusion.
For that matter, Asuka has developed such a streak of credibility that she could win the championship on her first night by beating anybody in the women's division and it would seem like it makes sense, even if her opponent is Charlotte Flair or Nia Jax.
New Champs in WWE! More RIGHT HERE
If Asuka is going to be away from NXT long enough that a new champion needs to be crowned, instead of doing the interim champion method, the developmental brand can simply move on without Asuka.
The Empress of Tomorrow can be forced to relinquish the title due to her injury so she saves face as still never having lost it, as her undefeated record is intact, allowing NXT to declare a new champion without factoring her into the mix.
Then, to avoid having to lose to the new champion in NXT, Asuka can heal up at her own pace and when she's ready to return to in-ring action, she can simply be drafted to Raw or SmackDown and start anew on either of those shows.
This gives Asuka the transition to the next level of her career that she deserves while also removing any hindrances of NXT's show and the talented women who can still hold that division down and make it a huge success even without their dominant champion.