Hartley will survive as captain either way. Jamie George is certainly a better player but Hartley is Jones' man and his experience probably puts him as our no.2 option in my eyes so he'll stay. Until atleast next 6n. Ironically I can see a failure to make the lions actually helping his England captaincy chances as no one will have a chance to fill in in his absence. A strange one that! Slightly off topic, but Hartley and Farrell both make the lions who will captain in the summer. Billy and Brown are the vice captains but both may well tour and if brown doesn't is he actually caption material? Haskell maybe? Launch?(again if he doesn't tour), robshaw? (Is that even tenable?)
It could be a great opportunity to develop a new leadership group, but as I said maybe not great for Hartley!
Edit - thinking about it, it's quite likely to be who doesn't make it out of youngs and care due to experience, but if Eddie wants to develop a new SH or two it could be interesting!
Brown is definitely 'caption' material - what the caption is depends on what you think of him ... I imagine a few people will have some creative ideas :lol:. Whether or not he is
captain material is definitely debatable.
In all seriousness, the captaincy for the Argentina tour will be interesting.
You've covered most of the realistic contenders in your post, but I think there's a good chance most of these will make the Lions squad. Hartley is probably touch and go at the moment, but I think Gatland likes him. From England's 'vice captains', Farrell and Billy are as good as nailed on Lions, so that leaves Brown as the least likely of these to tour.
On the other hand, I don't think that makes him the next choice as captain as I think Eddie definitely has the desire to experiment with other options for the 15 shirt in Argentina and the AIs.
Launchbury and Itoje would be contenders but will surely be Lions? Youngs is probably more of a maybe, but I think he'll go too so Haskell and Robshaw are the obvious options to be captain. Eddie will want to experiment with the back row, but if we lose 10-15 players to the Lions, then I can imagine him wanting to keep some experience in the side. Robshaw probably won't want to do it, so if Hask isn't picked for the Lions, he'd be my pick.
Other than that, it really depends on who tours with the Lions. Someone like Kruis could be a contender. Lawes has the experience but is too quiet. George would be another with a decent shout, but again, I'd back him to tour with the Lions.