My team (of five) and I currently support 700+ Cassandra nodes across 30+ clusters in production. We use Spinnaker to help manage Cassandra in our external cloud. If a node gets blown away, it does replace it on its own.
You do want to keep a close eye on it though. If the replacement node comes up with a different IP, the old node will still be in the cluster (just
DN). So at some point you'll need to
nodetool remove it manually. Also, if multiple node failures happen at once, you'll need to make sure that it doesn't try to bootstrap more than one node at a time (which will also fail).
The bottom line, is that there are other tools like Spinnaker that can help with much of the heavy lifting. But it's not magic, and there is only so much "auto-healing" that it can do on its own.