So I just watched the extended promo again and noticed something. At 0:55 seconds when we see Nick with the 3 bodies outside the cabin, there are actually 4 bodies. Right before that clip ends, at the very bottom next to Nicks Toyota there is a pair of legs and hands that can be seen for a brief glimpse. The leg length indicates male and the color of the jacket the person is wearing is a mid dark blue. The same color that Sean is wearing.
That's 4 out of the 7 remaining Grimm gang.
You're right, good eye!
Trubel is also wearing black so it could be her that died. Also Eve was also wearing black in some of the promo pics. Heck most of them are wearing dark clothing (theme of the show).
I was able to print screen and zoom it and reference it to the image # 9 from the top. So it does seem like Sean.
If you watch the trailer and some of the pics, Eve is not at the cabin with them, she was at the Spice Shop and face to face Zerstorer, most likely she was killed.
So from how it looks, it could be Nick, Adalind, Diana and Kelly survives.
On the other hand it could be just a nightmare/dream for Nick just like what happened to Diana!!
I'm also good if Adalind and Nick AND Eve (if she gets her Hexenbiest back) will live happily ever after! Yes the three of them! :). Dark times they need to have some powerful offsprings! lol.