Slimelung death despite recent treatment

You probably cured him too late the damage has been done

That indented text in the tooltip is a description of the disease, not of the current state. "Death in 10 cycles" doesn't mean Rowan would die 10 cycles from now, but that Slimelung causes a death in 10 cycles (from the moment somebody contracts it).

llunak is right, this a description of the disease, not the duplicant. One additional thing to note is that the 10 cycles is cumulative for every moment the duplicant does not have the Received Treatment buff. So if you treat them at 7cycles to die, after the treatment wears off, the duplicant will have 7cycles to live.