Same thing happened back in 2010 for a while and then they came back:
Users of online map want their MTR exits back | South China Morning Post
baidu maps have exits
百度地图
but only in chinese
HERE Maps also have the exits:
https://www.here.com/?msg=Wan Chai S...f=geoexpat.com
The labeling/contrast is not so good (at least label the exits and bus stops with a different color), but it does the job and Apps are available for Android/iOS/Windows.
Mobile app Citymapper has MTR exits and is quite a nifty app to get you around town.
The MTR exits are showing up on Google Maps again