In trying to be balanced on this subject and not to be dogmatic, it would seem justified to pull the plug when all else has failed and you have peace from God to do it. If you do not have peace from God, then do not do it. We all have heard of those that have come out of very critical situations and have gone on in life. Probably in most cases it would be best to wait it out. To be sure that you have peace from God, I do not it is presumptuous to have at least two or three agree on this. I think that the principle of (Mt 18:18-20) could be applied in relationship with a witness of the Holy Spirit within, because the issues of life and death belong to the LORD. If you have to make that final decision, with peace in your heart from God, no matter how your heart may condemn you after the fact, God is just and is greater than your heart and knows all things (1John 3:20).
We can also believe God in this:
Psalm 116:15 'Precious in the sight of the LORD is the death of his saints'.