All of these crypto functions have many implementations in every popular programming language that return the exact same bits no matter which implementation you use. As long as you have the keys (which is a serious issue) and someone remembers which function was used with which parameters the risk of "will be left with a bunch of HTML files with data that the browsers cannot decrypt anymore." is not even on the same scale as getting hit by lightning but rather on the same scale as getting hit by lightning during clear weather in a deep basement.