AFAIK, you can leave it off for ages, turn it on and... continue as if nothing happened. You'd surely miss tons of gameplay (because that's what comes with this kind of scripting), but you wouldn't lose your game over it.

Just regard it this way: there's a lot of EB which makes it different from anything else, such as graphics, sounds, descriptions and other stuff - but what really makes the difference is it's script. Without the script everything else is reduced to mere 'candy', nice, and indeed good in it's sort, but, without the 'framework' that the script provides the mod loses it's backbone, nerves and muscles. You'd simply have Vanilla restyled.

(You'll have noticed that I strongly recommend you turn the script on. )