Not all superheroes rely on superpowers to establish themselves in the hero business. Of course we have characters like Batman and Hawkeye that don't have any powers. Sure Batman has his incredible mind and detective skills but that's something he trained himself for. Many heroes have powers or gadgets that enable them to wear a brightly colored costume and take on the villainy of the world.
Supervillains will stop at nothing to accomplish their goals. If anything, we've seen lately that they are willing to go further than they have before. For superheroes, fighting evil has become more deadly than ever before.
For the heroes defined by their powers and use them to fight crime, what happens if they suddenly lose them? Over the years, the heroes should have picked up other abilities to aid in their fight but what happens if they become an ordinary human? Would they still have the possibility to stay in the superhero game and fight deadly villains that would kill them without a second thought?
As seen by a few examples, being a superhero doesn't mean you have to have superpowers. Let's take Wonder Woman, for example. She is the champion of the Amazons. She is capable of going toe to toe with the likes of Superman. Besides her magic lasso, tiara and bracelets, she has the sheer power to smash any foe that stands in her way. There was a time she gave it all up (because of her love for Steve Trever, who was being framed).
Wonder Woman was summoned by her mother. The Amazons had to leave our dimension in order to rejuvenate their power (it was the 60s so just bear with me). Wonder Woman decided to stay behind, which meant performing the Amazon Rite of Renunciation and relinquishing all her mystic skills and garb. She was left with the powers of a mere mortal...until she met I Ching. He needed her help in defeating a common foe and offered to teach her the skills she would need. He offered to teach her...Karate.
Wonder Woman was adept under his instruction and mastered the art within a few short months. For several issues (from 1968's Wonder Woman #179 to 1973's #204). She proved that she was more than just her Amazonian powers and magical items. She continued to fight crime and evil using her body as a weapon.
Karate and Kung Fu is a common weapon for the hero without superhuman abilities. Powers are something they are usually given and rarely involve any upkeep or honing. For the characters that rely on hand to hand fighting skills, like Batman, even becoming a master doesn't excuse them from training.
After Batman recovered from getting his back broken by Bane, he pretty much had to retrain his body. He had a long road and despite recalling all the moves he had learned, he was going to have to train once again. Thus, Batman went to Lady Shiva to undergo an intensive round or training to become the fighting machine he once was.
After Batman died and returned, he also wore a special technologically advanced suit in order to check on the Bat-family in the guise of the Insider.
Wonder Woman and Batman weren't the only ones that were Kung Fu fighting. Recently, even Spider-Man has taken to learning some martial arts from Shang-Chi, Master of Karate. Spider-Man isn't exactly depowered but it turns out everyone in New York City is gaining spider-powers that rival his own. And after getting trounced by Spider-Woman, who has had had hand to hand combat training courtesy of SHIELD and HYDRA, Spider-Man decided that he also needed an edge to add to his fighting arsenal.
Captain America is another hero that relies on his hand to hand combat skills. In the mid 90s (in Captain America #438), the Super Soldier Serum in Captain America's body apparently gave out. Cap had lost the use of his muscles after years of use and pushing himself past his true limits. In order to prevent being completely paralyzed, Tony Stark implanted biochips into Cap's body and created an exoskeleton suit that could control his movement.
The exoskeleton wasn't the answer to all of his problems. His heart was weak and could give out on him at any moment. Rather than sit back and wait for that possibility, Captain America ensured he would be out fighting until the bitter end.
There are plenty of other heroes that lost their powers. Take all the mutants that lost their abilities after M-Day. Many of them did simply give up but some such as Jubilee, Beak, Angel Salvadore and Chamber got power suits of their own and became part of the New Warriors. Losing their mutant abilities didn't mean they had to stop trying to save lives.
There is also Hal Jordan. He may have picked up on some hand to hand fighting skills being in the Justice League along with Batman but he's always relied on his Green Lantern power ring and his strong will power. Not that he's been stripped of his ring and is no longer a Green Lantern, it's that strong will that tells us Hal is far from being out of the game. He most likely won't pick up a power suit or start mastering Karate, but he is sure to find a way to regain a power ring.
Superpowers for superheroes makes it a lot easier for them to fight the supervillains of the world. There are some heroes that do not have superhuman abilities and rely on other methods to give them an edge over the bad guys. For those that suddenly lose their superpowers, if their heart is it, the loss of powers doesn't mean the end of their careers. For them to continue being superheroes, they just need to find a way to adapt to their loss. The need for heroes is too great as the villains are becoming more and more deadlier each day. Today's heroes should prepare for the eventuality they lose their powers. Unless they are willing to accept defeat, their job won't be done until they have rid world of evil.