User blog comment:It's Good to be the Queen/The Thrill is Gone/@comment-5102537-20130105135348/@comment-5674726-20130105172800

All we know is that Arthur will rise again when he is needed but we don't know why and what Merlin contributed to it.

Technically, all we know is that Kilgharrah has claimed that Arthur will rise again when he is needed. Maybe he believes what he's saying but considering how the prophecy about Arthur creating a united Albion with magic restored worked out, I wouldn't be inclined to take his word for it.

By the looks of the end of the finale, Merlin is spending his immortal life waiting for things in Britain to get bad enough for Arthur to have to return to sort things out. Considering that civil wars and two World Wars weren't enough, either something much worse is supposed to happen in the future, or Arthur's not coming back.