Demilitarization of Ukraine and Ukraine not in NATO could have been a bargaining point but Trump gave it as a gift to Putin. Though I highly doubt Putin would have accepted anything less than that after all the lives lost.
 
The only bargain left is of size of land. The deal could be Donbass and Zaporizhzhia east of Dnieper river given under Russian control and the region of Kursk occupied by Ukraine and Kharkhiv occupied by Russia exchanged.