There have been many, many threads on this topic in the past, and many people have reported doing CESAs from 100 feet and beyond. It is not at all unreasonable to expect to do it successfully.
A couple of points:
Yes, the expanding air will provide you with air throughout the ascent, even if you are not rushing it too much.
You should have a full breath to start because you will know you are running out of air. The regulator will get harder and harder to breathe from on those last breaths, so you should have ample warning that you are on the edge.
Your tank is not out of air. Your regulator must be able to provide you with air at a pressure above the ambient pressure of the water around you or you cannot breathe it. When that pressure falls too low, you cannot get the air. Ascend to a shallower depth and (thus) a lower ambient pressure, and you will get air from the tank. That is why you do not discard your regulator or hold it in your hand. Keep it in your mouth where it can do some good if needed.
Put the last two points together. If you realize through labored breathing that you are almost out of air and start our ascent, you might be able to use a normal breathing pattern all the way to the surface.
Finally, watch your gauge and stay with your buddy and this whole thing will remain nothing more than an internet debate.
A couple of points:
Yes, the expanding air will provide you with air throughout the ascent, even if you are not rushing it too much.
You should have a full breath to start because you will know you are running out of air. The regulator will get harder and harder to breathe from on those last breaths, so you should have ample warning that you are on the edge.
Your tank is not out of air. Your regulator must be able to provide you with air at a pressure above the ambient pressure of the water around you or you cannot breathe it. When that pressure falls too low, you cannot get the air. Ascend to a shallower depth and (thus) a lower ambient pressure, and you will get air from the tank. That is why you do not discard your regulator or hold it in your hand. Keep it in your mouth where it can do some good if needed.
Put the last two points together. If you realize through labored breathing that you are almost out of air and start our ascent, you might be able to use a normal breathing pattern all the way to the surface.
Finally, watch your gauge and stay with your buddy and this whole thing will remain nothing more than an internet debate.