I'm guessing that your guess is incorrect, given that I AM a programmer (and someone familiar with FET's code for that matter), but I understand what you're getting at. Obviously it's not just a swap-in replacement, and even someone working on a relatively simple project like a Ren'Py VN would need weeks if not months to familiarize themselves with the existing codebase. Same with hiring a second coder, unless they're working on distinct parts of the game independently (e.g., someone on the map system and someone else on the minigames), it tends to become a managerial clusterfuck, especially with small "internet" projects.
On the other hand, that's still better than the alternative of having NO programmer at all. The worst case scenario we're looking at here is basically "guy takes 2 months off, decides that he's done anyways and quits". Hence why it makes sense to plan for that possibility, however remote, just in case. The team having a budget of 20k and only two members is kind of an anomaly.
I'm also a bit cynical when it comes to believing that he's been spending these grueling, 80 hour work weeks nonstop for the past 4 years just to make the game happen, given the amount/quality of the writing and the code, but let's not get into that. I genuinely do hope he takes the time he needs and things can get back to normal.