Raditz criticised Goku for having his tail removed at the start of Dragon Ball Z. At the time, a Saiyan's tail was thought to be their ultimate source of power, though this has since altered. In any case, Goku has no intention of growing his tail back.
While Raditz thought this was stupid, Goku had his reasons for chopping off his tail. Even if he later regrets his decision, there may be ways for him to regain his appendage if the necessity arises. But first, it's critical to understand why he withdrew it in the first place.
Why Was Goku's Tail Removed?
Goku's tail was a double-edged sword for all the good it did him. If someone grasped it, it would deplete his vitality and render him useless. He finally overcame this flaw, although it was still a poor one to have.
More importantly, seeing at a full moon would transform Goku into a Great Ape and send him on an insane rampage. His Grandpa Gohan was killed during one of these rampages. In this way, Goku's appendage rendered him a danger to himself and anyone around him.
The only ways to get Goku out of his Great Ape form before he hurt somebody were to cut off his tail or blow up the moon. Master Roshi was once forced to perform the latter option. As for Goku's tail, it would regrow if it was given enough time.
Goku eventually found a permanent solution to his tail while training under Kami. The Guardian of Earth agreed to use the Dragon Balls to restore the moon if he was allowed to remove Goku's tail. The procedure was never shown, but Kami made sure the appendage would never grow back.
The Saiyans' capacity to regrow their tails has always been ambiguous in the narrative. The prevalent notion is that it can return while Saiyans are children, but that capacity is lost when they reach adulthood. This is supported by Goku's and Vegeta's experiences. The latter is important since advanced alien technology doctors actively attempted and failed to repair the prince's tail.
The only sign that Saiyans can regrow tails later in life comes from Dragon Ball GT. Goku got his back after undergoing special training. This new tail allowed him to mix his Great Ape and Super Saiyan forms to become a Super Saiyan 4. However, this instance is questionable. Not only was Goku regressed to a child when this happened, but GT has been rendered all but non-canon.
Could Goku's Tail Ever Come Back?
If Goku and the other Saiyans chose to, they could conceivably reclaim their tails. Whatever is keeping them away now, it should be easy to wish them back with the Dragon Balls. If Super Saiyan 4 is ever retconned into the current canon, the live Saiyans will be able to access it.
Until then, it should be presumed that the Saiyans' tails are permanently gone. Whatever transpired, none of them will receive anything until a particular procedure is used. However, the combination of Super Saiyan 4 and a Dragon Ball Super unique power-up is an intriguing proposition.
