I mentioned on one of the many other threads about this same topic how to implement an auto-attack to keep everyone happy.

Add an auto-attack skill that can be added to your skill bar. It will provide a basic attack that uses no stamina and generates no TP and will continue to attack until another skill is used. Implementing it ths way keeps the combat involving and allows people to get attacks in when they've no stamina, while still making people work for their TP.

Implementing an auto-attack any other way would require reworking stamina, TP gain, and almost every attack buff skill in the game, plus it would also require all mob AI to be altered to include auto-attacks.