The court date was set for Monday a while back and deliberately set to ensure that Johnson would be held in contempt if he failed to comply with the law. Which he has -- not signing is irrelevant, the side letters will be ignored, the EU has immediately recognised it as a legitimate request for delay. So there is now not much to say or do in court on Monday. Remember Cherry was speaking after Johnson's reply in parliament which seemed to imply he was going to break the law, but then he rolled over like a Poundshop Trump and did what parliament had instructed him to do.
As ever with these things legal twitter is your friend :
https://twitter.com/davidallengreen/status/1185699948475617280
If one must read journalists, avoid Peston, Laura K., Shippers, etc. and go with Sky's Beth Rigby :
https://twitter.com/BethRigby/status/1185668023635628042
IMHO much the drama will be in parliament and what the speaker will do with regard to Rees-Mogg's questionable approach to running the order and business of the house.