You're better than you think @barborrico. I'm a bit drafty and @byteball.market's clarification is better than my own answer π
Indeed, stability point would not progress.
The user, if honest, could - theoritically - discover a partial order at the cost of a big travel back in time until last witnesses posts. This effort could keep the unit unsable a lot of time independently of new posted units by other users.
Worst, there will have no definition of rendez-vous point allowing user to synchronize/merge his path until the genesis unit with a stable chain. Result will be total chaos and systematic redefinitions of the best path will occur. By itself, the path is not deterministic and bifurcations are always possible without the witnesses.
In plus, if there are suspicious units posted that require the total order to be deemed valid, it will be the drama.
I need a coffee πͺ
Thank you both !