I'm skeptical it'll be added back as well, but we can hope.
How well the ABL performs depends on a couple of factors. On the 2018 LGs, ABL doesn't kick in until ~150nits on a full field white image. SDR is mastered to, and generally intended to be viewed at a peak brightness or luminance of 100nits (+/- 20nits) in a light controlled room. By light controlled room, I mean a room in which the display isn't being viewed with a lot of ambient sunlight or can at least use curtains or blinds to mitigate it. In those parameters, 150nits should be plenty bright. Keep in mind though that most real world content doesn't feature scenes equivalent to a full field white pattern that often, so the ABL isn't likely kick in as much as you might think. The higher the percentage of the screen features bright content, the harder the ABL works. So for example, if you are watching a night scene in a movie, the moon and stars should be as bright as you've set the TV's peak luminance or the "OLED Light" on the LG (SDR peak luminance can be up to 345nits with OLED Light at 100). If the movie then cuts to a day time scene on a snowy mountain, then the ABL will kick in preventing anything on screen from being brighter than 150nits. You should also know that the higher you have peak luminance set for SDR, the higher your risk is for burn in. Granted the risk isn't that high for normal usage anyway, but a higher setting will still increase it.
ABL affects HDR content in a slightly different manner. With SDR, how bright a scene is (or objects in a scene) change relative to how high the peak luminance is adjusted on the TV. HDR is different because luminance is absolute, so you can't (or at least shouldn't) be able to change the peak luminance and thus the overall brightness of the image. Further, full field white is not supposed to be higher than 100nits; it's only the highlights or certain small object that are supposed to get higher than that. As such, ABL can sometime be less of an issue for HDR. There's a reason that OLED TVs still win HDR shootouts against LCDs.
Fortunately, when the ABL engages, it isn't usually noticeable most of the time. There was, however, a bug on the 2018 LG's awhile back that caused a slight delay before the ABL activated. When it went from one scene where the ABL was off to one where it was on, the screen would slowly dim after the scene change. With how ABL works on most displays, you shouldn't be able to see it dim like that as it's supposed to be instantaneous (and thus mostly imperceptible). This has since been fixed with a firmware update and it functions as normal.
From my own experience, modern OLEDs are virtual light cannons compared to my Panasonic plasma. The ABL was far more aggressive on it where full field white maxed out at ~35nits. Even still, it wasn't too bad with real content. Since peak brightness topped out around 150nits (IIRC), it could still get plenty bright for most content and didn't bother me most of the time. It was only in comparing it to Samsung's last plasma (which activated ABL at ~80nits full field) that I realized how dim the Panasonic could be. The ABL on the 2018 LGs (the 2019 models aren't any different to my knowledge) really isn't that much of an issue under normal viewing conditions, but you situation may be different. I'd suggest checking them out in person if you can to help give you a better idea of what it's like.
