I don't have the numbers, but a portion were not removed. What happened to them might have a few clues to the fate if all had remained.
I don't know about other areas but the remaining in Indiana fell into two groups. The first and documented group were those assimilating faster. These had acquired title to land, either through the early territorial treaties, purchase, or a homestead claim. This group usually had a working grasp of English language, or were fluent, were often literate in English, or French (or several languages), had a grasp of US and state law, and usually had adopted settler style agriculture or acquired a trade. Many were at least modestly successful businessmen. This group evaded or were not required to be Removed. They continued to assimilate into mainstream rural and small town Indiana culture. Tho many retained knowledge of the ancestors and some continued the tribal/religious rites.
The other group were small family size groups who were able to evade the removal unnoticed. They usually lived in isolated marginal areas, less desirable for settlement. They continued in a impoverished subsistence farming living supplemented with hunting, were often illiterate, and assimilated with other impoverished subsistence farming families. Their knowledge of their ancestory was hazy or forgotten.