What happens if we lose a front-row player and can't contest scrums?

Under World Rugby Law 3.13 to 3.18:

• When a front-row player leaves the field (injury, yellow card or red card), the referee asks at the next scrum whether your team can continue with contested scrums. If you say you can't, the referee orders uncontested scrums.
• Scrums also become uncontested if either team cannot field a suitably trained front row, or if the referee orders it.
• Uncontested scrums caused by a send-off, yellow card or injury must still be played with eight players a side.
• If the player comes back, or another front-row player comes on, contested scrums may resume.
• Another player may play in the front row only when no replacement front-row player is available.
• At the match organiser's discretion, a player whose departure caused uncontested scrums may not be replaced, and a further player may have to be removed.

SA Rugby's Scrum Law Modifications also require uncontested scrums in adult rugby to be played eight a side.