I doubt that many failures on grand randonnees can legitimately be attributed to the bike. The probability of finishing would not seem correlated to equipment choice since the DNF rate hasn't changed all that much over the decades during which time equipment has changed quite a lot. The Rohloff won't matter one bit either way in my opinion. Get it if you want it.
Things like knowing how to be comfortable riding in cold, wet hills probably matter more although starting with the determination that you will finish also matters.
I did see a Rohloff on a custom brevet bike on a 300K. It had fashionable thin tubing said to plane very well. It was one pretty Randonneuse. It was a cold, rainy brevet with snow coming down at higher elevations. I think 2 finished it. One was a fixed gear and the other was 11 speed SRAM Red.
You did not ask specifically, but I would focus on versatile, warm, "rainproof" kit and getting yourself and bike as light as practical but it has to be comfortable and reasonably durable. PBP does not have any steep hills but my Garmin recorded almost 39,000 feet of seemingly unending rolling terrain that starts to feel hilly on the old joints at some point.