Is it a condition for the acceptance of the repentance of one who sent messages containing aid to polytheism (shirk) and forbidden acts that those messages be deleted, or is repentance valid along with the sin for its effect? And is the deletion waived if it entails hardship?

We fear that the question might be about waswasah (whispers/obsessive thoughts), but if the messages are not seen by anyone and no harm is feared from them, then their deletion is not obligatory. However, one should strive in this matter for fear that their device might fall into someone's hands, and those who are susceptible to being influenced by them might see them. He must regret what he has done, advise those he messaged, clarify the reprehensible content in his messages, strive to replace his evil deeds with good ones, invite people to Allah with insight, and frequently write what benefits people, for "Indeed, good deeds do away with evil deeds."