Hurd had taken a medical leave of absence earlier this year and it's likely that Oracle was prepared for this (1)
Safra Catz, the other co-CEO, will run Oracle in the meantime. Ellison intends to appoint a new co-CEO in the near future(2)
(1) https://www.mercurynews.com/2019/09/12/oracle-co-ceo-mark-hu...
(2) https://techcrunch.com/2019/10/18/former-oracle-co-ceo-mark-...