Is ghusl necessary after insulting the Divine Being and then returning to prayer, or is seeking forgiveness sufficient?

Cursing Allah Almighty is apostasy. The one who does it must repent sincerely, utter the two testimonies (Shahadatayn), and regret the sin. It is more cautious for him to perform ghusl (ritual bath), to avoid the disagreement of scholars who deemed it obligatory, such as the Hanbalis and Malikis.