This thread's been done before in the spring.
Obviously you'll die. I mean I seem to be the only one that remembers that thread, so I can only assume from that all the other folk that took 29ers to the alps were taken out in a wheel explosion and I'm the lucky exception to the rule. The guy with me on a solaris was obviously haunting us and actually dead, I mean you couldn't ride a 100mm 29er hardtail in the alps could you?
More seriously: what a daft question. What's wheel size got to do with it? Type of bike and the trails you want to ride matter more. My XL horsethief was fine on trans provence trails, alp d'huez, port de soleil, les arcs etc. Would other bikes have been better? Yes, some times other bikes would be better, sometime mine was best. This is always the case. I'm looking forward to taking it out to the alps again.
If you have to ask the question, maybe the real question is: "how does the rider get on with steep techie stuff?"