Ett bra försök, pias!! In some contexts, this is perfectly Ok, but I thinks that "till det verkliga slutet" is a good translation for "usque ad ultimum finem".
This expression is often followed by a genitive case in Latin, for example, usque ad finem mundi (to the end of the world), usque ad finem vitae meae (untill the end of my life), usque ad finem terræ (to the end of the earth), etc.
Cf. Ecclesiastes 3:11 (ab initio usque ad finem = from the beginning to the end)