It should remain as it was, falling off or not as appropriate.
RAW, as far as I'm aware, only discuss equipment when shifting into Wild Shape, and I'm not familiar with any rules that describe anything with respect to the reverse. So from a "things do what they say they do" perspective, nothing special should happen to the beast equipment.
A creative DM might rule specific effects on a case-by-case basis: barding might stay on but be very uncomfortable when reverting forms, and might require help to remove. A saddle might just fall off. Ape-shaped boots might be way too big, or might be too tight considering the Druid's own, already-equipped boots. Horseshoes might remain partially nailed to the Druid's feet, or might fall harmlessly to the ground as the hooves disappear.
There are a lot of edge cases from other arrangements, particularly effects similar to the Druid's equipment merging into the animal form. For examples:
- What happens if the Druid turns into a horse, is shoed, and then later Wild Shapes into a bear? Are the
horseshoes still on, but inappropriate and not helpful? Are they not
part of the "bear's" form, and so they don't appear?
- What if the Druid turns into a horse, and later Wild Shapes into a horse, but a different
horse? Are the horseshoes on the new horse?
- If a character adds equipment to a beast form which would alter its
ability to deal or avoid damage, that beast form's CR might change.
Would that fully-loaded form then cease to be an option to Wild Shape
into again, because the equipment makes its CR too high? Or might the
player have an overpowered, deluxe beast form available after kitting
- What happens if a Wild-Shaped Druid puts on a backpack, or worse, a
Handy Haversack or Bag of Holding? Are the bags, and their contents,
unavailable until the Druid transforms back into those specific
shapes? Can a Druid offer essentially infinite, perfectly secure storage by
Some of these effects could be pretty dramatic but are not described or referenced at all in any published material, and so I would be hesitant to assume (RAI) that anything like them is possible. I would revise my opinion with a specific citation to the contrary, but my knowledge of the rules suggests that donning equipment while Wild Shaped and then reverting to normal form should have no mechanical effect of any kind.