Longtime lurker stopping in just to relay my story in case it helps you and anybody else :-) Sorry I don't have answers and statistics for your specific question. I know it is incredibly frustrating to hear when all you want and need is a crystal ball, but every birth can be different, even within the same woman.
With my first, my water broke and nothing happened. I hadn't found MDC yet, but I knew I wanted an intervention free birth. Unfortunately, I didn't know much about homebirth at that point, so it was a hospital birth that ended up having every intervention under the sun and ultimately a c-section. For what it's worth, my super medically minded doctor did "let" me go for (if memory serves) over 58 hours with my water broken because she did know how much I wanted a vaginal birth. But eventually I started developing a fever despite being on antibiotics for GBS and he started having the bad decels in his heartbeat. Like you, I think he was positioned poorly and if we weren't in a hospital there may have been a chance.
Then my second birth I had found MDC, prepared like crazy, hired myself a doula, and found a dr. that was much more natural minded. I did a lot of soul searching about homebirth, but ultimately decided to go the hospital route again. Well didn't you know it, it happened again. Water broke (at work no less) and absolutely nothing happened - again. With the coaching of my doula, I tried every way to get labor going - even castor oil, but no - not even a twinge. I even fibbed a little to my dr. about when my water actually broke. For what it's worth, my doula (actually she was a monitrice (sp?)) said I would've "timed out" of the homebirth midwife she worked with, so I'm glad I didn't opt for homebirth. So, 24 hours later I went to the hospital. No GBS this time, so no antibiotics for that, but my dr. was getting antsy about the time (and he didn't even know about my time "adjustment" that really would've made him twitch). So I had zero interventions this time, but about 40 hours after my water broke nothing was happening and I was dialated zero cms, so I was just frustrated and done and tired of getting pressured, so I consented to another c-section.
At this point I was convinced my body was, indeed, broken, but I am stubborn. We decided to go for #3. With the help of some MDC mommas and ICAN, I found a provider that would let me try for a VBA2C. I took a sh!t-ton of vitamin C (supposed to help strengthen your membranes) and all kind of things to make sure I was GBS free again, my blood pressure stayed low, and I didn't fail the 1 hour GTT (didn't ever before, but I wanted there to be no complications). I listened to hypnobabies VBAC disc, to boot. So two days before my due date I felt a familiar gush of fluid. Craptastic. So I went to bed to try to relax and get some sleep (this is the ONLY thing I didn't do after the first 2 times my water broke prematurely). And wouldn't you know it, about 2 hours later LABOR STARTED!!! I was so freaking excited. At first they were coming 5 minutes apart and not too strong. They quickly progressed to 2 minutes apart and got stronger but I reveled in the pain. So off to the hospital we went, about 4 hours after labor started. Stop reading here if you want to imagine that I went on to have my triumphant VBA2C....ok I warned you. Anyway, even with the 4 hours of regular contractions I got to the hospital and I was only dialated to 1 cm - BOO! Had some interventions that didn't go over well, and ended up with my 3rd section, but the point of my story is that I was sure I would never go into labor on my own, but I did, and the fact that I did was so incredibly healing to me - I wasn't completely broken (though I also don't seem to dialate on my own, but with patience and better support the first time, I may have eventually dialated and had myself a baby the good old fashioned way). So don't give up or assume anything. Hope my personal experience helps a little and good luck with your future VBAC!!! Oh and sorry I wrote a novel. I tend to do that