I believe if they're able to move fast enough they'd wouldn't be on Russian territory long enough for Ukraine to lose their moral position. Sorry if I wasn't clear, their goal is not to invade Russia, it's only a problem with the plan, that attacking from the North down would, at first, force them to squeeze between Russian territory in the North and Russian held territory in south-east.

Their end goal in this would be the complete recapture of the Luhansk region. Forcing Russia to send in re-enforcement from the South and West.

I believe like everyone else they'll attack the center, in the South. Still, if you can pick up a bishop and a few pawns ;)...