Is repentance considered valid if the repentant person does not regret their past sin (alcohol addiction) due to their joy at being guided and their bad deeds being replaced by good ones, given that they have abandoned the sin and are determined not to return to it?

Regret is a fundamental pillar for the validity of repentance. If you do not regret your sins, your repentance is invalid, and your evil deeds will not be transformed into good deeds. Therefore, you must regret what has passed from you, while resolving not to return to the sin.