I think he will return with the mask. I can't remember if the first promo was before Sin Cara's injury or not (don't follow wrestling so often these days like I did when I was younger). But if it was after, I find it intriguing that at a time when WWE say sales of masks are at their peaks (holiday season) they begin to advertise a Kane return suggesting he comes back with his mask. Kane comes back before/after Christmas, at the ideal time when Christmas has been, people get gifts or receive money, and then release the Kane mask on the WWE shop. Profit from that.
Of course I could be entirely wrong and this could've been long in the planning. I would hope he grows his hair back or wears a wig if he does return with the mask, and that he sticks to the theme he has been using. I don't see a point in going back to his older themes when the current one would fit the character with a mask.