Duty & Courage! No matter the cost.
More than a few stoics were wiling to risk exile or execution in their opposition to tyrannical behaviour. Helvidius Priscus, a senator during the reign of Vespasian, is just one of many examples of stoics who did not yield to tyrannical behaviour.
Helvidius made it apparent that he did not see eye to eye with Vespasian, even refusing to address him by his imperial titles. He believed in the supremacy of the senate: requiring the emperor to seek guidance and obtain senate approval on matters of state. He would go on to defend his role as Senator (fulfilling his duty) and promote constitutional principles in defiance of the emperor.
"If asked, I must say what I think is right!"
Helvidius to Emperor Vespasian
Epictetus recounts a specific confrontation between Emperor Vespasian and Helvidius before a meeting of the senate (Discourses 1.2 18-2). In it, Vespasian confronts Helvidius warning him to stay away from the senate...and to refrain from speaking if he does attend.
Helvidius responds saying that as long as he is a member of the senate, he must go in and that if Vespasian refrains from asking his opinion, he will not speak. Vespasian tells him that he must ask his opinion and Helvidus counters: "If asked, I must say what I think is right."
Clearly angered with this affront to his authority, Vespasian warns him that to do so will result in his death.
In a classic stoic retort, Helvidius responds "When did I tell you I was immortal? You will do your part - I will do mine. If I am to be banished, I will depart without sorrow; if I am to die, I will die without fear." Sadly, Vespasian had his way and Helvidius was forced to commit suicide.
"I will do what is expected of me. I will let nothing stand in my way..."
Marcus Aurelius, Meditations 6.22