Imagine that I’m a druid, wild-shaped into a beast. I got polymorphed by a wizard. I want to know which form my druid will revert to when the polymorph spell ends because of the wizard losing concentration: my normal form or my wild-shaped form?
Let's look at the description for Wild Shape:
You can stay in a beast shape for a number of hours equal to half your druid level (rounded down). You then revert to your normal form unless you expend another use of this feature. You can revert to your normal form earlier by using a bonus action on your turn. You automatically revert if you fall unconscious, drop to 0 hit points, or die.
So there is a time limit, your free will, falling unconscious, going to 0 hit points, or dying.
- Time limit:
- The polymorph spell lasts only an hour at best. But the spell was ended early. So unless you were already well into your one or more hours of Wild Shape, this should not be a factor.
- Bonus Action choice
- Did you use a Bonus Action to revert back? Now, just because you dropped Wild Shape while polymorphed does not undo the polymorph spell. But it would affect the shape you revert to after the polymorph spell ends.
- Falling unconscious/0 hp/death
- It sounds like you were still awake/alive when the wizard dropped the spell so these are not factors.
So unless you used a Bonus Action while polymorphed or were well into the time limit of the Wild Shape, there is no reason to believe you would have changed back to normal form. You should revert back to your Wild Shaped form.