Webcore itself isn’t going to die: it will continue to work in its groovy incarnation with some other platforms. They have their own forum, so you can see more about that over there.
The groovy version that works with smartthings will go away when the Samsung hosted free groovy cloud goes away, just like every other groovy smart app.
As to how much of the functionality will be replaced by the new official feature, the rules API, it’s just hard to say yet. That is still in development.
We should also note that the original author of Webcore was hired by SmartThings A couple of years ago but has since moved onto yet another company, so he is no longer available as a resource. But Samsung has many other talented developers.
You can read more about the new rules API in the following area of the forum. “recipes” are their version of “pistons.”
If you have a specific piston that you can’t figure out how to re-create with the new architecture, you can start a thread under automation ideas and someone may be able to help. 
And for more information on the hub’s role in the new architecture:
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