Russia has sided with the Iranian Shiites against the Sunni terrorists, who currently are running Libya. I suspect that may be the real reason.
Russia opposed the NATO attack on Kaddafi led by Obungo, which installed the al Qaeda terrorists running things now. So the guys currently running Libya probably have no love of Russia, and just wanted a convenient excuse to kill or expel them.
The terrorists who were the successors to Khaddafi in Libya have turned that country into another Palestine, an ungoverned and largely lawless territory.
There is no longer any ambassadorial function in that territory. It has devolved into whoever can hold a defensible position against the next attack.
And the attacks will just keep on coming.
My guess would be that there is little to be gained for Russia to keep an embassy open there except as a base to run its network of paid informers. But I’m sure Libyan spies are iffy at best in times like this.