Sorry! Back to the original question.
The approved procedure is discontinued when it has been fully completed. If crew decide on safety grounds to discontinue the procedure, that does not seem too unreasonable to me. If the procedure is discontinued for other reasons, the crew may have some difficulty later defending such a decision.
If the procedure specified after a certain point that the remainer was for separation or airspace requirements, I believe following a reasonable ATC instruction would then be acceptable but not otherwise. What is "reasonable"? Depend on circumstances. If you are very familiar with the area and procedures, you are using first language of yourself and controller and radar environment with transponder altitude capability, reasonable is easier to define. Take away some of these more agreeable circumstances and deviation is more difficult to justify. Unfortunately complience is also more difficult.