It will not be easy for FSB to just remove him, they would need some convoluted plan and make sure someone would not tell Putin about it, on the other hand Putin can get any inconvenient individual poisoned or thrown of a window.
I could be wrong but FSB is kept in check by Putin private army branch, the main army is kept in check by the mercenaries, the mercenaries are controlled with money, the oligharchs are controlled with fear of FSB dudes killing them. So you would need all those to coordinate to eliminate Putin.
IMO largest changes would be a military intervention after Putin gives them some idiotic order like killing ethnic Russian civilians or some extreme suicide mission.
I could be wrong but FSB is kept in check by Putin private army branch, the main army is kept in check by the mercenaries, the mercenaries are controlled with money, the oligharchs are controlled with fear of FSB dudes killing them. So you would need all those to coordinate to eliminate Putin.
IMO largest changes would be a military intervention after Putin gives them some idiotic order like killing ethnic Russian civilians or some extreme suicide mission.