Interesting question, but I cannot think of a reason to justify answering it. When we look to statistics, it is to have some basis for prediction. Can anyone say that an individual has a XX% chance of returning to the derech? I suggest that not, since there is a huge number of variables involved, and the true determinants are the factors involved for each individual. But it can good discussion, even though there is no practical value to it.
The other part of the problem here is the age old question. “What is the derech?” The typical responses are woefully inadequate (I’m being overly kind – they are probably terribly misguided). Does returning to wearing the proper levush the indication of return? How about Shabbos? The questions go on. These issues might all be valid ones, but what truly indicates return to the “derech”?