I agree with OS, and that to avoid any ambiguity, the term Cancel SID could have been used. After all, once you'r airborne not only are you flying a specified track but you are maintaining a minimum climb gradient. If ATC cancel or take you off a SID after departure they are basically vectoring you and therefore assume responsibility for terrrain clearance ( not allowed below MSA) ; so, if a revised deparure heading is required from ATC it should have been planned for and the term cancel SID passed before, and separate from, the take off clearance, along with new departure instructions. At least this is the case in Oz. I appreciate that this isnt the case world wide. And thereby lies a potential problem of miscommunication/ muisunderstanding. This is not standard ICAO as ICAO dont promulgate words to this effect in either DOC 4444 (ATM) or DOC 9432 ( Man of telephony). Its a National procedure. On the other hand Continue Heading is ICAO and appears to be widely used. When considering just the use of actual RT, if ATC told me to Continue or Maintain I would have understood their intent, but would have also queried the instruction due to the considerations outlined above.
DogGone