I'm a windows user, so I'm not sure if the icon can be restored using Get Info, but that's the first thing I would try. Find one of these files, right-click on it and Get Info, then scroll down and I believe you'll see someplace something like Opens With and an option to apply to all files of this type.
I'm pretty sure Peter's suggestion should be the way to rebuild the associations again on a Mac.
It doesn't work, unfortunately.
The only thing so far that works is to Get Info, Copy the icon from the top bar (it only appears there or if you press space on the file to preview it) then paste it in the icon space.
That only does it to one, and I have millions of ID files in all sorts of folders, so even doing batch icon changes would take a while.
I'd suggest asking your question on the Apple forums in the Yosemite forum. It sounds more like a Mac OS X problem, really.