It is clear that Ukraine has no future without Russia. This enormous and unpayable debt is just one of the many reasons why. The good news is that if (or rather when) Russia wins they won't need to pay it. Whether Russia takes it all or just installs a friendly government in Kiev, the debt will be defaulted on either way. The obligations to the West that this current puppet regime entered into will be denounced as illegitimate as the regime itself was illegitimate.
Not a problem: once they achieve their maximalist goals, they can auction off the regained territories to foreigners to pay for the cost of achieving their maximalist goals.