Even if the brain was "alive" after the blast, unconsciousness would have been immediate, I think.
I say, we check for the answer to that question with Mr. Max Headroom...room...room...
The old story is the executioner at the guillotine would pick up the head and show it to the body. At that point, the eyes would go close. Reportedly this was because the slice was so sharp, such as when you slice your finger with a very sharp knife and don’t realize it for a few seconds.
According to highly reputable Internet searches:
Once your heart has stopped, and you're clinically dead, you'll be well beyond noticing anything that's happening to your body. “After the heart stops beating, oxygen supply to the brain is cut off,” Claudia Hammond noted on BBC. “With no glucose store to rely on, nerve cells die within three to seven minutes.” So that really is it.
Said searches quickly mentioned stuff I didn't want to know and were stopped.