Midway through Cave Story, near the end of the Labyrinth, there is a room with a single door placed across a large gap. After entering the room, Professor Booster falls from above and lands offscreen in the pit below.
If you jump down and talk to Booster, the Professor will die after giving you the Booster 0.8 jetpack. This will also make the game’s best ending inaccessible.
For the best ending, you need to jump over the gap and leave Professor Booster behind to fend for himself. Later Booster will appear alive and well in Mimiga Village with an upgraded Booster 2.0.
Is it ever explained how Professor Booster survives the Labyrinth if you leave him behind?