Almost certainly it will not work if BUG is not initialized, unless some reprogramming is done.
The way the event handlers are loaded requires BUG to be loaded first. The CvFinalFrontierEvents.py file doesn't have anything in it anymore, for example. The event handlers are in FinalFrontierEvents.py and loaded by BUG. I expect this could be changed back, but it would take some effort and a knowledge of Python programming. It also loads the callback functions in FinalFrontierGameUtils.py via BUG and without BUG it would not use those, just the ones in the regular CvGameUtils.py which is missing the programming that makes a lot of FF work.
I expect there are also other things in the Python that do not check to see if BUG has not been initialized and try to do things that won't work if it isn't. When I added BUG in, I did it in the easiest way possible which was to just to add it in with no checks to see if it was actually being initialized.
I'm not sure what all it requires in addition to the event handlers being loaded. I expect there are some graphics functions (UI elements such as the scoreboard and the bug options button itself) which could be a problem. It needs some of the functions from BUG for other things too such as FinalFrontierEvents.py uses the BugData functions to store information across saves, although I don't know if disabling BUG would have any effect on that as long as you left the file it loads to do that where it is (assuming you fixed it to load that that file in the first place, as it is currently loaded by BUG).
In general, I see no reason to disable BUG enitrely. You should be able to turn off any features of it that you don't want to use via the BUG Options screen. There might be some things that are not controllable this way but the only one I can think of is maybe the BUG Options button itself (and it might be possible to turn that off, I don't remember). So if there is some feature you don't want to use, you should be able to just turn it off. TC01 has said that he turns most of it off. It should remember your settings.