The title could be misconstrued that Google groups is going to be discontinued. It won't be for a long time, simply because Google heavily relies on it internally.
They killed Google Code in 2016, and Google Code Search in 2012. Internally those types of products still exist, just not for public use. I see no reason Google groups could not also be killed for any public use.
I’m not sure that’s entirely accurate. As far as I understand the internally available equivalents are entirely different products than what was publicly available, and have never been made public themselves.