I love Google Fonts - I use them with nearly every project I work on in some capacity. I've used TypeKit in the past as well, but always preferred Google's system.
I've become increasingly paranoid about Google shutting down systems since they did away with Wave, a thing I actually used and integrated somewhat into my workflow (apparently I was the only one). But all in all, I'm not paranoid about them shutting down webfonts. Here's why:
Google Domains, & Google Cloud Computing.
It's not all that hard to see that Google is starting to get into the consumer hosting business. Within the next few years, you'll be able to host your site with Google - and not a cheesy Google Sites page either, I mean the real deal. Google Domains is a pretty clear sign of this, even without all of the other signs over the years.
Keeping Google Fonts around is just one step in building what could be an excellent "website builder" in the vein of SquareSpace. It'd also be a (I think) huge source of income: hosting your site on Google would sound like a great way to Optimize for Search - even if it did nothing on the SEO front, it'd sell for that reason because people wouldn't care. They'd see "Google" and just assume.
Which is great.
Google Domains is the best domain system I've used in the last ten years. It's clean, efficient, incredibly nice to work with. I use Namecheap generally, and as good as it looks on the outside, it's management interface is still stuck in 2005. Google Domains doesn't have that problem - it's modern and great. That gives me hope that their other tools in that vein will have those same traits.