What happens if they cancel or get a refund?

A cancellation ends future commissions from that person. Everything they already paid, you already earned; nothing is taken back.

A refund reverses the commission on that payment. If it was still pending, it simply goes. If it had already been paid out to you, your balance goes negative by that amount and comes back up as new commissions clear.

Partial refunds

A partial refund reverses the whole commission on that payment. One rule, applied the same way every time.