To resolve yes, both reactors must be shut down at the end of the day on Dec 31, 2025. As in no longer operational - a temporary shut down, e.g. for maintenance, does not count.
https://calmatters.org/environment/2023/03/diablo-canyon-nuclear-power-plant/
Federal regulators today granted an exemption that will allow the Diablo Canyon nuclear power plant to stay operating while it pursues permission to keep operating past 2025.
The decision by the U.S. Nuclear Regulatory Commission means Diablo Canyon can keep running under its current license as Pacific Gas & Electric seeks full approval to extend its lifespan. PG&E has until Dec. 31 to submit its renewal application, which must outline issues related to safety and integrity of the aging reactors.
PG&E said it will seek permission to keep the plant, now slated for shutdown in 2025, operating for up to 20 additional years — the full extent that is customary for a nuclear power plant application.
But state officials have not indicated that they intend to allow Diablo Canyon to stay open past 2030. Under a law passed last summer, SB 846, Unit 1 can keep running through Oct. 31, 2029, and Unit 2 until Oct. 31, 2030.