Hello,
First post here, but I hope I can offer some help nevertheless.
I have not come across much evidence for this topic in secondary sources, but there is a short chapter in G. Wensch-Klein, Soziale Aspekte des römischen Heerwesens in der Kaiserzeit, F. Steiner 1998, pp. 88ff. - provided you read German. The chapter is available online at Google Books
here. As usual, footnotes and bibliography might help.
I short, we don't seem to have much evidence beyond the fact that, after an examination by doctors and a "competent judge" (iudex competens) the soldiers would receive their
honesta missio and the regular benefits of a veteran (C.I. 12,35,6 under Gordian). The author goes on to say that we don't know what fate awaited them afterwards, but she cites an example where Pompey settled his veterans and invalids in Nikopolis. Wensch-Klein suggests that the military camaraderie would allow the invalids to fit in, rather than end up being ostracised by society.
There's a few more details, but that does seem to be the extent of research to my knowledge but similar chapters may exist on other books dealing with wider themes relating to the Roman army.
The idea that they would end up in the settlements around the camp and the military colonies, if they were lucky, seems reasonable. How much their comrades would have helped them along, and whether there was an equivalent to the funeral funds they could draw from, seems conjectural.
I'd be very interested in hearing the results of your research.
Best,
M. Caecilius
(Max C.)