character is in a unit, the units gets destoryed completely, but the character survives; 1: if he flees, does he keep running since his unit isnt over 25% or noore
No, once the unit is gone, it is gone. The character stands on his own. I am not sure about if there were a couple of the models in the unit and the character though.
so when a unit is destroyed completely, just the character survives, and he flees, i am stil able to rally him?
Yes you can rally him, as he isn't in a unit any more and he is of course not below 25% as he is a single model. If the units gets destroyed its no different from leaving the unit, no rules of the unit applies any longer.