"To come true" means to be become reality. When a wish comes true, it goes from a wish to being real. The wooden puppet Pinocchio wished to become a flesh-and-blood boy and his wish came true.
Given that, it is not clear what "come untrue" would mean. The wish went from a wish to...what? Did it remain a wish? Or did the wish come true in part but have an undesirable element? For example, the poor man became rich, but he got very ill.
It would be an enigmatic title for a work of fiction, but that's not necessarily a problem.
P.S. Here is the affirmative statement in the simple past:
The wish came true.
The negated form is:
The wish did not come true.
We use auxiliary "did" + not + bare infinitive "come" to produce the negated past of affirmative "came".
Here is the affirmative in the present-perfect:
The wish has† come true.
† In centuries past, they said "is come", using "is" as the auxiliary with the past-participle "come".
The negated form using the present-perfect:
The wish has not come true.
has come untrue would be ungrammatical, and nonsensical. It might nonetheless be used in a title for a literary work, where it would be understood to be an intentional violation of grammar (compare the poem by e.e. cummings that begins "Anyone lived in a pretty how town"). It might be thought to be playing on "untied". We can say
His shoelace came untied.
His shoelace had been tied, but then it became untied.
But we could not say
The food came uneaten.
unless we were in some magical world in which digested food could miraculously reappear on the table again after it had been eaten; or unless we were trying to find an unusual circumlocution for "was vomited".
We could say
The food came uncooked.
The food was not pre-cooked, but was raw, and needed to be cooked.
These are all different meanings of the verb "to come".
come true ... come untied ... come uncooked
A tied shoelace can become untied. But cooked food cannot become uncooked. Similarly, a dream that has come true cannot then later become untrue.
A wish goes from dream to reality as the raw becomes the cooked.
So, if you want to say "This is a world where every dream comes true", you can say it affirmatively:
All dreams come true
Every dream comes true.
If this is a world where everyone remains disappointed:
No dream comes true.
I'm not encouraging you to use the double negative. That is your arbitrary requirement. But if we accept the requirement, to state the affirmative as a double negative, we cannot use stative "comes" but must resort to a stative + passive construct:
No wish stays ungranted.
[Compare: No food remains uncooked. Food does not cook itself. Wishes do not grant themselves.]
But that would be a rather clunky title for a work of fiction. So we change the statement to a mere fragment of a sentence, a simple noun-phrase:
No Wish Ungranted or No Wish Unanswered