Does that mean that Google now has no more use for Gmail, and soon millions of people will be scrambling to cover yet another product sunset?

That would certainly cause an enormous loss of goodwill, but.... imagine this scenario:

Google has some slow growth quarters, they need to keep the numbers up for shareholders. They start to examine what they can squeeze. Gmail costs them X (hundreds?) millions per year, but doesn't gain much from it...

Certainly its unlikely, as it is also a SSO tool, etc. Still....