Chai_18
Before going into your core question with regards to extending ones life despite it being clear from a medical and scientific stance that there are no chances for long term recovery.
You mention pain, patients do not need to experience pain, it can and should be managed well. And can also include managing their anxiety as well.
With regards to resuscitation or supportive care for none viable patients, this is a complex halacha question and needs people that are knowledgeable with the medical and halacha reality and is usually dealt with on a case by case basis.
But in general, we value every moment of life even if the patient cannot enjoy life or fully function. It can also be that patients don’t have a right to end their lives or to refrain from being treated (this pertains to halacha, in general patients have autonomy and can decide on their own for or against treatment as long as they have complete mental capacity).
There are organizations that deal with these issues.