Not only that, this sets a dangerous precedent: What happens to backgrounds, emoticons, cards and badges for games that get delisted due to licensing issues? Will those get removed when a big company decides to yank their game because they won't want to pay the licensing anymore? (cough CODEMASTERS cough ACTIBLIZZARD cough)
As far as I can tell, nothing happens to marketplace items when a game gets delisted. The owner of the game would have to go in and separately delete those items as the Hero Siege developer did. However the fact that it is even to be able to be done is a huge oversight on Valve's part.
In the comments, he states that he wrote to Valve and asked them to change his emoticons and they told him the following:
*Edit: Apparently it's just a canned message you get when you try to modify an existing asset, as
someone on his forum called him out on pretending he contacted Valve 
but the intent is the same that they really don't want people messing around with existing market assets.
Valve said:
Unfortunately, once a trading card set has been published on the market, assets cannot be changed because doing so would cause serious issues for users who have already earned them. Apologies, and thank you for your understanding.
So clearly they understand that this is undesirable behavior toward the existing owners of those items for obvious reasons.
Now logic would dictate that if it's bad to
change the existing items it's equally bad or worse to be able to delete them, but this is Valve we are talking about and they never quite think shit through before they create systems or make changes.
*Edit2: Apparently the old emoticons
like this one are still on the market but if you buy them you can't use them and just waste your money.
Someone on the forums said he just bought one and got nothing in his inventory.
k
:bow:
