What happens to gentiles if they break the 7 laws.
'Even though the Talmud and Maimonides stipulate that a non-Jew who violated the Noachide laws was liable to capital punishment, contemporary authorities have expressed the view that this is only the maximal punishment. According to this view, there is a difference between Noachide law and halakhah. According to halakhah, when a Jew was liable for capital punishment it was a mandatory punishment, provided that all conditions had been met, whereas in Noachide law death is the maximal punishment, to be enforced only in exceptional cases.'
-- 'Jewish Concepts: The Seven Noachide Laws' @Jewish Virtual Library
Noachide Laws were collected with their explanation in Maimonides' Sefer Shoftim ("Book of Judges") in the last section Hilchot Melachim U’Milchamot ("The Laws of Kings and Wars") chapters 8:9-9-10:12. For the teaching of the Talmud and the 3 laws that were liable to capital punishment, see Babylonian Talmud, Sanhedrin 57a.