Has this ever been proposed?

Has it ever in the long history of chess been proposed to allow the player to take his own piece if this rescues the king? That would be very much like in real-life wars. For example, in a smother mate, the king sacrifices (that is, removes!) one of the pieces that surround the king and the king escapes to a safe place. This seems to me an obvious possibility. Has this ever been proposed in chess? If this is allowed, many checkmate situations would allow the king to escape, but the penalty would be the loss of the piece.

doesn't seem like a good idea. Would turn completely drawn games into won games, and completly remove the idea of a checkmate.

This has been proposed many times, and the main reason it's rejected is given in post #2.
There is UCI engine called sneaky chess which would allow you to make an illegal, except the capture of the king, once per game. After playing many experiments, I found the first to take their illegal move usually lost.

If you want to introduce a real-life condition, let's ransom the king then the game could continue after checkmate.

Everything which would ruin chess has been proposed a zillion times.

In real-life wars,competent Kings (and generals) always make sure they have an escape-route in place.
Darwinism takes care of the rest of them. :)

You certainly aren't the first or the last one to propose this.

You can't post in the forums yet. Play some games!