#4 Relinquish the title but stay in NXT
Perhaps WWE doesn't wish to see Asuka on the main roster by the time she's able to return, or possibly ever — although the latter is highly unlikely.
In either scenario, whether Asuka is going to be out of action for a considerable amount of time or just a few weeks, there might be a way to get around having her give up the title but not actually transition to the main roster in doing so.
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Shinsuke Nakamura and Samoa Joe are both two-time NXT champions as well as The Revival for the NXT Tag Team Championship. So far, no woman has held this title more than once.
Asuka could be the first to do that by having her vacate the title only to win it back either from the next champion or from the vacated spot if WWE is able to stretch it out long enough.
She could continue her undefeated streak and also create another record for herself by being the only champion in WWE history (possibly wrestling history itself) to be undefeated, lose a title and then win that same belt for the second time without still ever losing.
Her dominance over NXT could continue for however long it takes until WWE has figured out the person they want to position as her successor, whether she loses the title to that woman or moves up to the main roster by being stripped of it like in the previous option.