Escalating without making an enemy

If a piece is genuinely not coming, tell the tutor or supervisor before the deadline rather than after it. Bring the record — what was agreed, what was asked, when — and describe the situation rather than the person. Most institutions have a process for this and can do very little once the work is already submitted.

Escalating early is not telling tales. It is what you would do at work, and the alternative is either a worse grade for four people or one person quietly doing five people's work — which is not a better outcome for anybody, including the person who stopped.