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 Kherson east of Dnieper river given under Russian control and the region of Kursk occupied by Ukraine and Kharkhiv occupied by Russia exchanged.

Regarding the use of natural resources in Ukraine territory post war, Zelensky could get a better deal if he talked straight to Putin but there's very low chances of it.