Becky: Fuck off.
James Conner: Don't talk to me that way. Your mother and I raised you better than that.
Becky: Life is fleeting. Life is short, too short. So you gotta use every moment. You have to do something that makes you feel alive, and that shit, that would spread that message far and wide.
Hunter: Don't you wanna punch fear in the dick?
Becky: What was Cactus Jack's name when he wore a mask?
Hunter: Mankind.
Answer: There's no indication that the ending is anything but real; the other twist in the film is heavily foreshadowed through dialogue, camera framing, and so on, none of which applies to the ending. A helicopter could have hovered above the tower and lowered a rescue basket/rope to Becky, as she's less than 100 feet from the very top. Given that the tower was probably constructed using a helicopter to position the final pieces of the structure (a common practice for communications towers of this height), there's no reason why it couldn't have held up. The tower itself is never shown to be weakened or compromised, only the ladder affixed to the outside.