I'm running out of fuel in space so my fighter got out of control, and I try to press some commands，But only this prompt appears “Wilt thou drift froever?!?
So i can't do anything in the game. What should I do to commit suicide and return to sosaria？

Try CTRL-Tab, which should reduce the game to a minimized window, which you can then close down. Relaunching the game should have you back at the launchpad, ready to start over.

(This game predates both DOS and Windows, so there's no way to shut things down from within the game, because there was no reason to. Back in the day, when you were done playing the game — or you had a similar problem like this one — you simply shut down the whole computer.)