If a wildshaped druid somehow got Undead Fortitude, would this prevent them from reverting?

Question

I believe this is completely outside the realms of RAW as I don't know of any way for a PC to gain Undead Fortitude beside homebrew,

Undead Fortitude reads:

If damage reduces the creature to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the creature drops to 1 hit point instead.

and Wild Shape reads

You automatically revert if you fall unconscious, drop to 0 hit points, or die.

So with these two wordings, if you drop to 0 hit points while wildshaped, and since you retain any features from your race, while wildshaped, does that mean that Undead Fortitude could prevent a wildshaped druid from turning back into its non-beast form?

Answer 1

Yes, Undead Fortitude would prevent them from reverting if they were to somehow acquire it.

As you said, undead fortitude states (emphasis mine)

If damage reduces the creature to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the creature drops to 1 hit point instead.

I would argue that because of the reading of this you would first make your CON save and if you pass you stay wildshaped because you are not at 0 HP. It is worth noting, however, that this could be up for debate; as Please stop being evil stated in their answer, Xanathar's Guide to Everything does include rules for simultaneous events which these could be considered.

If they are considered simultaneous, then the DM could say that whoever's turn it is gets to decide the order in which the effects activate and declare that you drop your wildshape before undead fortitude can take effect.

Answer 2

Not usually

Two things are happening simultaneously here, both triggered by having 0 hp. According to Xanathar's Guide to Everything, that means the person whose turn it is decides the order things happen in. Usually, you take damage not on your turn when an enemy attacks you, so usually they decide you revert first. If it is your turn, however, this does work.

Answer 3

It's Confusing

One interpretation is that because undead fortitude says "is reduced to 1 HP instead" means that it would take effect and you would no longer be at 0 HP for the druids wildshape ability to revert back to their initial form. Unfortunately D&D doesn't give us nice concise timing mechanics like Magic the Gathering, because that would bloat the rule book to hundreds more pages than it needs to be. So, we'll look at other abilities that function similarly, namely the half-orc ability:

When you are reduced to 0 hit points but not killed outright, you can drop to 1 instead.

But the Boar has a similar, although slightly different ability:

If the boar takes 7 damage or less that would reduce it to 0 hit points, it is reduced to 1 instead.

Now, there is some word choice by the Devs that imply that with both undead fortitude and the half-orc racial you do actually hit 0 hit points, while with the boar ability you never hit 0 due to the "If you would [...] instead" compared to the "When you are reduced to 0 [...] instead"

In the end, no, Undead fortitude doesn't prevent you from leaving wildshape

So the conclusion is that with undead fortitude you would indeed hit 0 HP which would kick you out of wildshape, but with the boar's natural ability you never hit 0. This could be an editing mistake, or perhaps the abilities were created at different times, but either way interpreting we're interpreting what is written.