How can one respond to someone who cites Umar ibn al-Khattab's saying to Hafsa, "The Messenger of Allah (peace be upon him) returned her for your sake," to argue that the Messenger disliked Hafsa and wished for her death? And are there stories that prove the opposite?

The divorce of the Prophet (peace be upon him) from Hafsa, and his subsequent taking her back, is established. This is mentioned in the hadith of Umar in Sunan Abu Dawud and Ibn Majah, and the hadith of Ibn Umar in Sahih Ibn Hibban. As for using this divorce to argue that the Prophet disliked Hafsa, this is false; for her virtue and status with the Prophet (peace be upon him) are well-established. Gabriel (peace be upon him) came to him saying: "O Muhammad, you have divorced Hafsa, and she is a frequent fasting person and a frequent night worshipper, and she is your wife in Paradise, so take her back." So the Prophet (peace be upon him) took her back. The divorce did not remove her from being one of his wives deserving of that status in this world and the hereafter. It was a revocable divorce, and then he took her back.