If Hopper jumped through the gate, he would just be in the Upside Down version of the Starcourt Base. I doubt he’d trek to Russia in the Upside Down, and even if he did, there’s a low chance there even still is a gate in Russia. The one time there was was in 1984, and that failed and immediately closed. I doubt that they created another one after they had already gathered the Russian Demogorgon and so many Demodogs from the Starcourt gate. I mean it’s not confirmed that the Russian Demogorgon and Demodogs came from the Starcourt gate but it’s pretty obvious.