Reread your tutorial letters and I think you'll find written in there somewhere that you shouldn't worry if there are problems with myUnisa on the due date, as the lecturers will be notified. I think all you need to do is just submit as soon as the site becomes available again; however, you'd better check that out for yourself, rather than just rely on what I think.
(We all know what Thought did, don't we? Thought thought he f@rted, but actually he sh@t in his pants. Old proverb.)