Long time reader, first time poster, former LEO...
I have family very close to the cabin, and in the surrounding area. I spent many summers there. The terrain is very dense, marsh/swamp, but the sandy soil would make tracking pretty easy, if she'd left on foot. The frustrating lack of detail or confirmation on several points seems troubling. I read all the posts, the FB threads, and MSM articles. Lots unanswered.
Signs of foul play, is a very vague statement.
Was oft-mentioned call from a cell or landline? Confirmed on both ends?
Person allegedly called thoroughly checked out? If not, then any cell activity or contacts between the time BF left and LE arrived, are important, unlike someone above's dismissal. Asked for "Help", again, almost useless.
All vehicles accounted for? Pets? Electronics? Weapons?
A FB poster mentioned an alleged domestic incident nearby, with vehicle description.
Another FB post from seemingly local, mentioned Animal Control, a gunshot.
Northern MI has become a large market for drug sales, and the specific area is private enough for grow operations. Any history for victim, BF, Ex, son, of troubles?