In short, a sunk cost is an expenditure made in the past that cannot be modified. Neither now nor in the future. A sunk cost is a cost that cannot be recovered. The English language has a nice expression to describe it in plain words: "There is no use crying over spilled milk". The milk won't flow back into the saucer pan. Many people nevertheless behave as if there was a hope that the milk would go back where it was.
The Sunk Cost Fallacy is an informal logical fallacy in which it is argued that the amount of time, effort, or money already invested in a project justifies the investment of yet more time, effort and money in order to complete the project.
This is a fallacy because the actual economic calculation which needs to be made is whether the project would be worth completing at the cost of the investment which still remains to be made.
Following the dictates of the sunk cost fallacy is sometimes referred to by the curious phrase "throwing good money after bad".
Martin Gerber's $3.7 M contract is an expenditure that cannot be modified. Neither now nor in the future. It is strange to hear mild justifications for keeping him as the starter simply on account of the money already invested by the organization. That money will be sunk whether he plays lights out for 70 games or pops in and out of the lineup in a backup role (unless you seriously entertain the notion for a trade of essentially equal value at this point in the season).
Ray Emery has earned the right to be the number one tender. Gerber will be a quite sufficient backup. Forget the contractual albatross and go with the winner. Does it need to be anymore complicated than that?