It was then-editor Margaret Clark. As soon as she saw the episode, she was unhappy with the outcome and saw the obvious way to bring Trip back, and she believed there was a story worth telling there. And, surprisingly, CBS Licensing had no objection to her proposal, presumably because the series was done and they had other licensed properties to focus on.
It's probably worth noting that this wasn't just a matter of personal preference. The tv show and the books had very different needs at that point. The show was free to kill off Trip, one of their most popular characters, because, what the hell, the show was history and they didn't need him anymore.
Pocket, on the other hand, still had an ENTERPRISE book line to sell, so they had more of an incentive to keep Trip around . . . .