Is it permissible for a Muslim who supplicates, implores, and relies on Allah for guidance, as stated in his question, to believe that he cannot be led astray from the straight path?

Allah's granting a servant success in supplication and worship is a sign of good and acceptance, in accordance with His saying, the Most High: "So as for he who gives and is dutiful and believes in the best [reward], We will ease him toward ease." So, whoever is inspired to ask Allah for guidance and seek His help, Allah will aid him and guide him, and he will be happy in this world and the Hereafter. And whoever persists in supplication and has good reliance and expectation, along with righteous deeds, Allah's favor dictates that he will not stray from the straight path. This was the state of the Salaf, who combined excellence and fear.