I know how you feel, it is 7 weeks tonight that my sheltie Bandit ran, he looks a lot like yours. I have learned a LOT from this experience, and one thing I have learned (from a university professor who studies coyotes WITH his tracking dogs), is that the coyotes are very unlikely to bother your dog. That was one of my big fears as well as we have a lot of coyotes here in Nova Scotia too. They prefer much smaller game, rabbits, mice, cats (sad, but true). He said they CAN go after a sheltie, but highly unlikely.
According to people I have talked to who are very experienced in this, the #1 threat is vehicles, but since shelties are a very nervous breed, they tend to shy away from busy roads. Not to say it can't happen, but not very likely. Knowing these two things really helped ease my mind a lot, as these were the two things I was most concerned about.
I've also been told that shelties go into 'feral mode' in order to survive, and because of this they can survive a very long time on their own, they are amazing at finding food, water and shelter, even in the worst weather. But their natural nervousness makes them one of the hardest breeds to find and catch.
I don't know if any of this info helps or not, but it certainly has helped me. Knowing all this has also kept me going, I am searching and working constantly, even after 7 weeks. I wish you the best of luck, I hope you get your baby home safe and sound very soon, I know how upsetting it is. If you want, I can post on here or email you & tell you what I've done in my efforts to find my Bandit. Maybe I've done something that you haven't thought of yet, maybe something that will help. I already emailed you once to tell you about this site, so you probably have my address, contact me anytime.