Admission into NATO will be so tough that it will be nigh-on impossible. It might even break the Alliance.
On current alliance laws, every state has to approve/accept the new member. We saw how long it took the safe countries of Finland and Sweden to be accepted, with both Turkey and Hungary blocking the bids and asking for their pound of flesh. With Ukraine, it will be 10 times that because the new member would bring a very realistic risk for the alliance of being immediately implicated in a war with Russia. Currently, unlike what many people claim, Ukraine needs NATO much more than NATO needs Ukraine let's be honest. And some states like Hungary and Slovakia (maybe even Romania soon) are captured by Putin sympathisers and apologists. There is no way they will sign Ukraine's admission into NATO, not without considerable stalling and huge concessions in a process that might take several years.
I think it will be more realistic to form another "coalition of the willing" which will need to involve the major European powers (Germany, France, UK) and the US as bare minimum, then include anyone else willing to take part. Then sign a legally binding deal between this "coalition", Ukraine and Russia to send peace-keepers and vow to defend the territorial integrity of the new borders of Ukraine. With any attack by Russia on those new borders leading to an "article 5"-style declaration of war by the whole coalition.