How do you deal with the fact that the large majority of the population in Crimea (and probably a lot of Donbas too) preferred union with Russia over staying in Ukraine? Do you deny them the vote for a generation? Ethnically cleanse them? Or do you give them a big hand on the rudder in the new unified Ukraine, like they used to have? Either solution seems like it's a powder keg for war to break out again.
So do war reparations, of course. That's basically how WW2 happened. As I see it, the best case scenario of Russia paying for all the damages is that it becomes an impoverished breeding ground for a lot of vengeful terrorism. Maybe you're more optimistic?
Also, is this peace agreement really more likely to happen if Moscow has been London blitz-droned into submission? When did your country last sue for peace in such a situation, and how long did that last? I don't have much sympathy for "political realists" in practice, but in theory, I agree with them that you should expect other states to behave like your state would have behaved.