Is it permissible for a man to supplicate to Allah Almighty to make his wife's sister his wife in this world, in the event of his current wife's death before him?

First: Praise Allah for your chastity and your struggle against your self to avoid prohibitions. Continue in this chastity, and put a strong barrier between you and your wife's sister.

Second: Do not wish to marry her as long as you are married to her sister, because this is forbidden in Islam. This wish is illogical and impossible to fulfill, and it is a trick of the self to keep the door of attachment to her open. So do not indulge in this wish, and do not turn it into a supplication, for this is a bad way of treating your wife, and not an action of rational people.

Third: Indulging in this wish and turning it into a supplication, along with your previous attachment to her, may lead to obsessive love (ishq). Obsessive love is a great corruption of the heart and soul; it is a psychological illness that corrupts one's religion, honor, mind, and body. Therefore, you must cut off these wishes and thoughts, rectify the affairs of your home, praise Allah for your wife, and cut off all means of communication with your wife's sister.