Joseph:
At the neshomoh level, a Yid who is not frum is no different from one who is. At that level, every single neshomoh is a child of HKB”H, as the Gemora states clearly (בבא בתרא דף י’ ע”א) that whether we are fulfilling Ratzon Hashem or not, בין כך ובין כך איקרי בנים. While I do not need to consider the Yid who is not keeping mitzvos a suitable shidduch for my child, I have no authority to address the connection he has to HKB”H. That matter is purely בין אדם למקום, and that is territory where I cannot trespass.
For that matter, the seforim tell us that teshuvah for anything is possible. However, someone else’s teshuvah is not accessible to me. I cannot base anything I do on it, and I cannot ever really know what is going on in that realm. If the OP’s question is otherwise expressed as: If I commit a major theft of enormous sums of money, which I will never be able to compensate, what teshuvah can I do? Valid question, since we are told that a prerequisite for teshuvah for גנבה or גזלה is the repayment. If the question is worrying about Madoff, or any other such individual who embezzled major monies, I suggest we redirect. If my personal חשבון הנפש is meaningful at all, I have enough work to do on myself, and have no business minding someone else’s חשבון הנפש.