Is leaving work in Saudi Arabia to return to Egypt and care for one's father considered a form of ingratitude for Allah's blessings?

Your return to your country to serve your father is not a sign of ingratitude for Allah's blessings. Ingratitude (batar) is arrogance, pride, and using blessings for disobedience to Allah, failing to be thankful for them. The ruling on your return to your father depends on his condition: If there is a fear of his perishing or suffering harm due to the absence of any of his children to care for him, and care cannot be provided through other means such as marriage or hiring someone to look after him, then one of you must stay by his side. However, if there is no such fear for him, then you have a choice between remaining in your country of work or returning to your father. Your return to him, while seeking reward from Allah, is among the greatest acts of filial piety. Allah may replace what you have with something better, for honoring one's parents is among the best deeds after praying on time. You should perform Istikhara (prayer for guidance) before making a decision.