1) An assurance that Ukraine will never be accepted into NATO, [presumably decided by some sort of NATO meeting with the power to make such a decision (?) ] would obviously have been perceived as a betrayal by the Ukrainian government, and rightly so. It would have been perceived, rightly, by Putin as a licence to do as he saw fit with Ukraine, which would this be implicitly recognised as his back yard.
He would then have proceeded to do as he saw fit with Ukraine; perhaps promising to stop doing so if the front line states were excluded from NATO.

2) Putin would have said "But you haven't stripped the front line states of their NATO membership, which I also demanded", and would have proceeded to invade Ukraine.

Neither of these two principal demands of his were acceptable. The fact that he has invaded Ukraine is in fact proof that it would not have been a good idea to accede to them.

As for your analogy(?) with Iraq, I'm afraid I don't understand it at all. What demands, what threats has the USA made against Russia recently? If I'm not sadly mistaken, it is Russia which was the demander, and is now the invader.
So, let's try it that way: "Putin and his cabal were on a mission to remake Eastern Europe, intending a short stop in Kyiv before they moved on to ..."

Actually, Saddam acceded to the coalition's demands and they invaded anyway.
Hum, this interpretation of your analogy doesn't do your case much good.

_{It is rightly acknowledged that people of faith have no monopoly of virtue - Queen Elizabeth II}