It's not about that. Yes, he could, but that was third o fourth time he would escape the death. When he agreed to go to that station he accepted the fact that he would die. He felt that it was his destiny. And perhaps he didn't want to risk and change smth.
Sadly, Charlie's death was necessary to trigger the long chain of events that lead to the Losties/Jacob's success over the smoke monster. With Charlie gone, Claire became emotionally Lost and this eventually led to the smoke monster 'claiming' her, and setting Aaron free to be brought up da Kate when they escaped (all thanks to Charlie turning off the blocking signal). All these things are what made the smoke monster so confident that he was indeed winning.
In actual fact, it was all masterminded da the Island and Jacob (and then Jack) to eventually trick the smoke monster into a situation where he became mortal and could be killed.
Charlie's death was a waste. If he really had to die, Desmond would never have gotten any visions in order not to tamper with it, it would just happen unexpected. Charlie could have jumped out of the cabina and he and Des could have swam up in time, but he wanted to fulfill his vision for the fear of Clare not getting rescued otherwise...Desmond did not need to tell him 'this time te have to Die...' That was a mistake and Desmond knows and feels guilty :(