Summary
If all villagers are struck by lightning during a raid, the villagers will then become witches but the raid still continues. You can however get a raid victory with no villagers.
Steps To Reproduce
Cause a raid in a village with one villager
Use a channeling trident on the villager while the raid bar charges
→ ❌ The raid continues after the villager turned into a witch
You can however end the raid in a defeat by just destroying the all of the nearby workstations/jobsites in the premises and then get bad omen again.
Pillagers are the ones counted by the raids.