"That is not possible!"
Translation:Tio ne eblas!
I would think that should be allowed, but it ultimately depends on context.
"Tiu" by itself (without the noun it qualifies) usually refers to a person or living thing. In such a case, use of "tiu" doesn't make much sense here.
But "tiu" by itself can sometimes mean "that particular thing" in which case I would think "tiu" is justified.
In the end, it depends on context. Since it is technically a valid translation (though not the most common), I would allow it.
it's from the international suffix of Latin origin, seen in „audible“ and many other words.
Does esperanto have contractions? Like n'estas for ne estas or n'eblas for ne eblas?
no, not for „ne“ (but „la“ and „-o“ may be omitted in poetry: l'arbar’ instead of la arbaro, etc.)