If you're using UI for Xamarin (iOS or Forms), this won't affect you. It's only the non-Xamarin product that's been sunsetted.
In fact, we've doubled down on development for UI for Xamarin. The new product name for this is "Progress Telerik UI for Xamarin.iOS".
I see that you've also submitted this question for Xamarin.Android, I'll reply there as well.
Lance | Tech Support Engineer, Sr.
Telerik by Progress
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Feedback Portal
and vote to affect the priority of the items