I am no scholar of Latin, but I am fluent in Spanish and English. Spanish is a variant of ancient Latin, which I believe died out because only Roman Catholic priests were permitted to learn it and speak it. The Catholic Church prohibited laypersons from learning Latin or speaking Latin. Hence it was never passed down through generations.
If you were to translate from Latin to Spanish, the phrase would read: “Si siempre era, entonces siempre será”
Translate this Spanish phrase into English and you now have this: “If it always was, then it will always be.”
Translating from Latin to Spanish and then from Spanish to English reduces speculation of how it would have read in English because Spanish to English is more straight forward, and Latin translates into Spanish quite easily because the words are similarly spelled and phonetically similar. This is not scientific but I am fluent in Spanish and English. Hope this helps.