If you want to import it, just as an image with colours, shades and stuff. You just need to take the illustration and open it on Photoshop, then just save it as a JPG that Sketchup can easily import. 2.-If you want just the Vector lines, then just export those lines with Illustrator to DWG or DXF, you can import this to Sketchup like any ACad File.
I’m sorry to tell you that I was unable to recover the file, even after spending an hour on it. It seems the file is corrupted.
Unless the gurus here make a miracle, I don’t think it can be recoverable. Another thing you could do, is to contact the by filling out the form and describing your problem. Since the form has a 5mb upload limit, I’d suggest including the link to your Dropbox file into the Issue Description box.
I can relate to a hard work of months being lost and know how you feel. There is still a tiny chance that others might be able to resurrect the file but also, be prepared for the worst as well.