lila23518, i was wondering that too on another question based on https://www.duolingo.com/skill/uk/letters-1/tips-and-notes
I would not say that it is an idiom. It's the quote from popular Ukrainian fairy-tale "Коза-дереза" (https://uk.wikipedia.org/wiki/%D0%9A%D0%BE%D0%B7%D0%B0-%D0%B4%D0%B5%D1%80%D0%B5%D0%B7%D0%B0), in which a half-crazy goat threatens different animals, listing them various injuries she is going to perform and finishing her tirade of abuse with "Тут тобі й смерть!". In that context the phrase can be literally translated as "And then (i.e. after I do all these things to you) you will die". Without that context "тут" is equal to present moment so I used idiom "at hand". With the same respect it can be said "You die now" yet I found it far not so expressive. In order to give better example, "тут" as time modifier can be equal to "then", "at that point" or "here" as the point of time i.e. this refers to action which goes after some context events. For instance: "Тут і казочці кінець" - "And here the story ends"; "Тут я все зрозумів" - "Then I realized everything".