The explanation behind the disappearance of Kate Kane would already be found by the writers of Batwoman.
The announcement of the departure of Ruby Rose from the series Batwoman took everyone by surprise. This above all raised a question: what future for the character of Kate Kane? While it was thought that the actress would simply be replaced and the change in appearance of the character put aside, the showrunneuse of the series made a completely different decision. A new heroine, Ryan Wilder, will take the place of Kate Kane and become Batwoman. A recent leak relayed by The Direct gives more details on the fate of Kate. According to them, the latter will die in season 2, leading Ryan to take over.
This same leak also mentions the introduction of an emblematic villain of the Batman universe in season 2. It is Jonathan Crane alias the Scarecrow. The latter would be responsible for the death of Ryan Wilder’s mother, what would push the young woman to become Batwoman and go after him. Ruby Rose having definitively left the series, the death of the character of Kate Kane seems to be inevitable and arguably the best option. It seems in fact not very logical that the vigilante decides overnight to disappear for no apparent reason. As for the Scarecrow, he is an interesting and clever villain who could certainly give a hard time to the new Batwoman.