The issue was never that it'd stop working completely. Instead, the API would limit the app once a certain number of requests happened, and charge for more. Since a lot of people use the app, there's a lot of requests, and it stops working quickly unless the developer pays.
Now that the app has been pulled from the market and it broke for everyone, it sees very little use. The limit doesn't get hit, and the app works. But if everyone starts using it again, it'll break again.
Edit: Just for kicks, I downloaded it from apkmirror and tried it. I very quickly got the 429 error when the API key has hit the limit.