It has been some time now since 'Room Lighting' was launched on Hubitat. I did migrate all my child apps from 'Motion and Mode Lighting Apps' to 'Room Lighting'.
Is it now safe for me to uninstall 'Motion and Mode Lighting'? Would Hubitat be eventually be removing Motion and Mode lighting to avoid the conflict of focus are between these two apps?
They have never done this, and I don't see it starting. They have sometimes hidden these for new installs (if you don't have the app added already) and in fact once did for some apps that Room Lighting effectively replaced. They also actually have for some things like Rule Machine Legacy (they backtracked on this Room Lighting-related change), but existing installs like yours would completely unaffected. There was usually at least one platform release of "warning" as well (say you wanted to keep it aa an option just in case but hadn't added it yet).
The above is also certainly accurate for your case: no difference if you aren't actually using it, even if you have the parent installed.
MML is depreciated and will not be getting any further updates. All functionality was moved over to RL basically right when RL came out. So yes I would say if you are not using it, personally I would remove the app just to de-clutter my apps list.
It was always safe to do so. It’s an individual user’s preference whether to keep using an older (but deprecated) app or a newer app with overlapping features.
As @bertabcd1234 said, the installed apps on your hub won’t disappear and should continue to function for the foreseeable future.