These are very personal decisions that should only be made by the patient (with informed advice from his medical team and caregivers), but I can't think of a situation where a PEG would not benefit the patient. It makes a huge difference in quality of life.
Speaking from experience, trying to take food or liquids in when your throat is determined not to let it go to your stomach is hell on wheels. The choking is exhausting, miserable, panicky ... add any nasty adjective you like. I am sure it extends life... in my case, it certainly has, but the big difference for me is keeping me strong, well-nourished and as comfortable as possible without stress. What a relief to have that problem solved.
As to the vent, this is even more personal, but I have read many trustworthy statements on this forum and elsewhere about the relief and improvement in comfort it can provide. Anyone considering either one should do their homework, but only the patient can say when enough is enough.