It’s not going to be easy at all, but it is going to be an easier financial struggle if Ukraine is part of EU, both for Ukraine, EU and even for future Russia. Reuilding will be cheaper and the bill can be footed up front.
Point is that it’s going to be an ongoing balance account rather than a direct loss account. EU doesn’t have to wait for Russia to repay Ukraine, as long as there’s an expectation that “most” of the money will be there.
EU don’t want Russians to be kept in poverty for decades due to war crimes of previous generations, so eventually EU will accept some financial losses and write off the balance to keep Russians from becoming refugees in Europe. Things don’t always cost what is charged, so there’s a lot of levee to negotiate in decades to come, while still making money and keeping everyone afloat. Contractors who do this kind of work know how to ask for prepayment and do price gouging, so they’ll be fine getting paid less than the suggested price.
I’m optimistic that things will work out, but it would be even easier if only Russia would accept the inevitable and cut the losses for everyone.