YES AND NO
Azeotrope mixtures do not break down, and behave like pure substances.
As for zeotrope mixtures, they do not always break down if there is a leak, for two reasons:
1 - The mixtures are made up of fluids of similar natures and as they have very small temperature variation they break down only slightly. In the case of a leak in gaseous state, simple refilling it reestablishes the mixture. Eg: R-404A, R-410A.