To make it possible Ukraine and Chine will need to redevelop many technologies that were used to build Mriya. The technologies were gone when USSR collapsed.
Not that many the bulk of manufacturing was done in Ukraine what was sourced externally can be sourced from subcontractors. For example engines are manufactured by Motor Sich (Ukraine based) which is still a fairly large engine manufacturer etc.
Hydrogen engines for Energiya, RD-0120, were made in Voronezh by KBKhA, which is still producing rocket engines. However this particular engine is practically lost - can't be recreated without extensive R&D program.
It's not enough to have the original manufacturer survive... Can Rocketdyne manufacture another F-1 today? So it's quite possible - though not certain - that Motor Sich wouldn't be able to create a unique enough engine, even if it did that in the past.
The engine is not unique to Mria it was used on AN-124 and Motor Sich has a modernised version going through testing Д-18ТМ so should not be any issues on that front