If the remaining money was in the Nazi’s compound, the police would find it. If it is hidden elsewhere, it is likely lost forever.
The fact that Walt shot Jack as he was using “I know where the money is” as a bargaining chip tells me that Walt must have been satisfied with the money he did manage to get to the family.
That was my take on it.
I had considered that.
In the beginning of the series he was looking for less than half a mil, so he had 20x what he got into it for.