it seems impossible in my point of view that the leaf will be useful forever : if people are never totally recovered where is the victory of God (and the victory of the saved ) ?
Hi Erwan
It seems impossible because, Scripturally, it is impossible.
The reason you must be thinking “forever” is from verse 5, where we are told that apparently his servants will reign for ever and ever. This must be wrong. Firstly, because the word “for ever and ever” is a translation of “into the eons of the eons”. The translators had a pretty huge problem if they translated it consistently with their “ever”, as it would have read “into the eternities of the eternities”. This is clearly ridiculous. So they made up a phrase “for ever and ever”. Because apparently “for ever” doesn’t quite cover it. 
But second, we know they can’t reign “forever” because Jesus will eventually subdue all things under his feet and then even Jesus will stop reigning (1 ?Cor 15:24). He will hand over the kingdom to the Father and God will then be all in all. (1 Cor 15:28)