Refuse to merge into their branch. If you have serious test coverage and the refactor doesn't change behaviour, it'll be fine.
If you don't have test coverage, or if the "refactor" is also changing behaviour, that project is probably dead. Make sure there's a copy of the codebase from before the new lead joined so there's a damage mitigation roll back option available.
If you don't have test coverage, or if the "refactor" is also changing behaviour, that project is probably dead. Make sure there's a copy of the codebase from before the new lead joined so there's a damage mitigation roll back option available.