I don't want to see you again! It's over, once (and) for all.
Are both forms acceptable? Is one of them old-fashioned?
Once for all is now old fashioned, once and for all being standard. The Oxford English Dictionary from ca. thirty years ago says "once for all, now usually once and for all".
OK, this thread is four and a half years old but I will put in my answer. "Once for all" is found in the New Testament in several places, whether you are looking in the King James dating back to 1611 or modern translations: Romans 6:10, Hebrews 7:27, 9:12, 10:2, 10:10 and Jude 1:3. It always means one time for all people. Christ died once for all. Of course, there is finality in what he did. When he had received the drink, Jesus said, “It is finished.” With that, he bowed his head and gave up his spirit. (John 19:30)