Does it include Wonder Boy III?
Via the wiki: Sega Vintage Collection: Monster World, called Monster World Collection (モンスターワールドコレクション) in Japan, is an Xbox Live Arcade release containing the arcade version of Wonder Boy in Monster Land (Monster World), and the Sega Mega Drive versions of Wonder Boy in Monster World (Wonder Boy V: Monster World III) and Monster World IV. For some reason it omits Monster World II, otherwise known as Wonder Boy III: The Dragon's Trap.
Strange that they included Sonic 1 and 2 considering they are getting de-listed. Although I'd like to think because they will be putting up the iOS versions eventually.
Despite being delisted, I'm sure several people own them. Plus, given how bad SEGA is at communicating internally, I would not be surprised if those making the games playable on One did not know of the delisting.