The L-rd said to Moses: "Come to Pharaoh, for I have hardened his heart and the heart of his servants, in order that I may place these signs of Mine in his midst, and so that you may recount to your children and grandchildren how I made a mockery of the Egyptians and how I performed My miraculous signs among them. You will realize that I am G-d."
Shemot 11:1-2
Despite G-d's intention to make a mockery of Pharaoh, the fact that He warned him that he would be punished for not complying means that, on some level, the door to repentance was still open. By hardening Pharaoh's heart, G-d had just made it difficult for him to repent--and since this was a punishment for Pharaoh's own obstinacy, it means that Pharaoh himself had made it difficult for himself to repent. But had Pharaoh nonetheless summoned the inner strength to listen to his conscience, he could indeed have obeyed G-d's will, let the Jews go, and spared himself and his country the ensuing debacle.
Now, Pharaoh was the arch-embodiment of evil in his day, and he had already deadened himself to G-d's call so thoroughly that G-d was punishing him by practically taking away his free choice entirely. Even so, it was still possible for him to repent, and G-d commanded Moses to remind him of this. How much more so, then, is the door to repentance always open to the Jew, who is rooted in holiness and goodness--even if it seems otherwise.
The lessons for us here, therefore, are as follows:
First, we must never succumb to fatalistic thinking. No matter how estranged we may feel from G-d, even if it appears that G-d has shut the door on us, nothing can resist sincere repentance. The apparent difficulty exists in order to inspire us to summon deeper and more powerful resolve.
Second, no matter how far another individual seems to be from G-dliness and holiness, we must never despair of him. The door of return is always open; all we have to do is find the right words, encouraging him to mend his ways for his own betterment, and with G-d's help he will come back to his true, inner self.
--From Kehot's
Chumash Shemot