Here's what earnest diplomacy would look like:

https://medium.com/p/5860e66da280

Have Russia sign a Budapest Memorandum 2.0 that gives Russia the same terms Ukraine signed on to in 1994: Russia gives up its nukes in exchange for all the signatories to Budapest 2.0 guaranteeing Russia's territorial integrity and security. What's good for the Ukrainian goose in 1994 should be good enough for the Russian gander now.