I'm not sure if the Save As dialog always presents you with the last file format that you saved, the next time you want to save. For me, it always presents Inkscape SVG. But then, that's about all I ever really save.
Actually I have saved other formats, such as PDF. Occasionally DXF or EPS for helping other people. And I don't recall having to change anything, the next time I wanted to save an SVG file. My best guess, without have any other evidence, it that Inkscape always offers Inkscape SVG as the first format to save with. But you still could have chosen DXF really without thinking too much.
Or there could be some difference here, between Windows and Macs. Maybe Mac does always offer the last format?
Well for recovering your original files, the DXF file still has all the paths. So you have not lost the paths. It sounds like the only thing you are missing are fills, right?
Just open the DXF in Inkscape, replace the fills, and save as SVG. Unless there's something I'm missing?