Axing Robin Hood

Yes and No.

Yes because Jonas was a great actor and no one could replace him as acting Robin and if someone did it would spoil the series.

No because I want to see what happens to the gang after Robin dies.

I think the show still had a little potential, even without Jonas. After introducing the Archer storyline I think they could have carried it at least for one more season.
But on the other hand, the show didn't have much to tell. It was hard enough without Marian and now without Guy.