Is it permissible for someone who has been tempted and gone astray to pray to Allah for guidance, and then for death, so that they do not return to their straying?

The general rule regarding supplicating against oneself is prohibition. It is permissible, however, in exceptional cases, such as fearing religious tribulation (fitnah). In such a situation, a person should supplicate to Allah for guidance and steadfastness upon the truth. It is also permissible for him to supplicate for death while adhering to the truth if he fears tribulation and a return to misguidance.