Is there an idiom that suggest you're giving an ultimatum to someone? Like something similar to "do this or you die!" although I don't think an idiom that use such strong language exist. Is there any idiom like that?
Informally, an ultimatum can be shortened to just:
Either an ultimatum or a very good offer can be summarized by the following example. You can replace "Al" and "Bob" with appropriate names or pronouns.
Al made an offer Bob couldn't refuse.