DBD won't disappear from Steam.
Nothing is happening to DBD on Steam. Steams policy prevents publishers from selling/exchanging NFT's in game. This Pinhead NFT is not minted by BHVR and is not in the game. The NFT is a limited run of blockchain created tokens associated with the character model and created outside of the game by a separate company. In fact buying the NFT does not guarantee in game content. If you read the website it says 10 out of the 10,000 NFT's will randomly come with access to the Hellraiser chapter. Those 10 people are basically getting Steam keys for the content.
Here's the difference. You buy the Hellraiser content for the game through BHVR (or Steam or GOG or Humble Bundle etc.) This is the in game content and is not an NFT. It has no blockchain information associated to it. What steam doesn't want is for a company to say you have to buy an NFT to get in game content, in other words the NFT is part of the game. This situation isn't that. The Hellraiser chapter purchased anywhere is not an NFT.