Standard operating practice would just be to move everyone else up a slot, and book some 'up and coming' band to fill the very early slot that's left vacant. Glastonbury managed to shuffle people between days when they lost their headliners a few years ago, depends who's free and who's got other bookings.

Looks like they had West headlining all three days, and I can't find anything about who else was due to play - Drake, maybe? The 2026 festival looks like a scam, how little detail there is about it.