Google's experiment with smart notification responses is winding down... although this won't be the last you hear of it. The company's Area 120 team has ended the Android test after roughly 10 months, noting that the work "will live on in other Google products." You can still use Reply for a few months more, but you could encounter glitches or less-than-ideal suggestions. Not that there's much reason to break out the tissues -- you can already see some of the benefits.
If you're using Android Pie, you should see some of Reply's notification features inside the apps you use. It wouldn't be surprising to see other features find their way into later Android releases. Either way, this was one of Google's more fruitful side projects and might pay dividends for many months to come.