ames – each case is so different. You must ask a competent Rav!!
Taking someone offlife support is so much more complex than signing a DNR/DNI with a Rav’s consent. I know of a case of someone with a brain injury on life support, eventually declared competely brain ead, etc. The family consulted with many rabonim. Taking the person off the respirator was NOT an option. However, there was an opinion that perhaps they might be able to allow the bag of IV medication to run out and not replace it with a new one. Thus they wouldn’t be actively ending life support, but rather it would come to a point where the meds would run out and they wouldn’t start a new bag (similair concept to not initiating intubation as opposed to removing the tube).