A new stream called stream 1 is created.
I deliver some changes to stream 1.
Later, I delete stream 1.
So:
Is there a possibility to restore a deleted stream?
Not easily unless you had created snapshots (we covered snapshots in your previous question "Consistency of snapshot code in rtc?"): in that case, when you delete a stream, RTC would ask you to select another existing stream in order to keep ownership of those snapshots.
If you do, then it is trivial to re-create a new stream from a snapshot, assuring you to recover all components at their exact state as recorded by the snapshot.
But if you didn't set any snapshot, then you have to manually re-enter all the components, and set them to (for instance) their most recent baselines.
If I am not able to restore the stream then, will I loose my changes delivered to it?
In any case, as mentioned in the thread "Delete a Stream - any side-effects?"
Change-sets exist independently of any stream, so deleting a stream does not delete any change-sets.
It will just be harder to get the exact list of change sets back to a new stream if they were only delivered to stream 1 (that you deleted).
Especially if those change set were never grouped inside a baseline (for a given component) or, as explained above, with a snapshot.
But those change sets are not gone.