I haven’t seen a WST statement yet, but going by the draw on their site, Ronnie and John Higgins have withdrawn and are replaced by John Astley and Hamim Hussain respectively.
It’s understandable, and both are safe for the 2021 Tour Championship.
John would probably find it difficult to be up for this best-of-seven from start to finish tournament, and Ronnie, I think, was showing signs of stress and fatigue. As Clive Everton often stated it does nothing good for him to “overplay”, and after yesterday’s defeat, he probably needs to step back and regroup.
Ronnie O'Sullivan 
Wow. They must be in the biggest scare to face Hendry. No, of course I agree with you Monique. Ronnies strategy to play in as many events as possible for practice reasons has probably backfired and he needs to regroup now very badly indeed after four consecutive losses in finals.