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?
Best Answer
Yes, Undead Fortitude would prevent them from reverting if they were to somehow acquire it.
As you said, undead fortitude states (emphasis mine)
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.