Do them look like roots growing near the top of the split?

I've plucked honeysuckle and other crud from damp crotches and splits in trees. My bet is water was getting into your tree, caused a damp moist spot as well as a weak point, something was taking root, and poof, here comes an odd wind and it comes apart.

Silver maples have their uses, like fast shade and decent fall color. They're shorter lived though (usually not six years!) so legacy planting isn't one of them.

What's your plan from here on out?

That looks like the leftovers of codominant stems, a situation where two essentially same diameter branches "join" with a very narrow angle between them.

The problem is that they junction is insecure because they lack the normal annual wrapping of the new layer of wood. One will always break free when just the right amount of torque is supplied.