What happens if I take revenge and destroy all the attacker's facilities?

If I get even with someone who attacks me, and I destroy all of his village, what is really seen on his screen? Have I really destroyed anything? Does it cost him? Aside from draining some of his resources, how else do I hurt him?

tl:dr You have not really destroyed anything other than sprung traps, but you have cost the opponent all resources and trophies you stole.

If you use the "Revenge" option on an opponent, it is no different than a regular multiplayer "raid" that you access from the "Attack" button, with the one exception being that opponents whom you attack with "Revenge" can not attack you back (they are not given that option, since they already attacked you once).

• What your opponent sees is the same thing they see as the result of a normal raid. Buildings and walls that were destroyed appear destroyed for the instant they load their park, but begin to rebuild instantly and are back to normal within a few seconds.
• Tombstones also appear on any unoccupied space where your units were killed by their defenses, and they will get a small amount of elixir for clearing them, although it's so small as to be negligible.
• Any sprung traps (bombs, spring boards, etc) - are lost permanently. These your opponent will have to pay to replace.
• The primary way a 3 star win hurts your opponent comes from lost trophies and resources. If leveled your opponents camp you stole the maximum amount of resources and trophies. Pretty much no matter what their circumstances, that is the worst outcome for them.

what is really seen on his screen?

Your opponent will see his village in ruins for a very brief period of time until the village is quickly "rebuilt". This is less than a minute, but they will have to wait before they use the buildings you destroyed.

Have I really destroyed anything?

You've destroyed any traps that you triggered and any troops you killed in the clan castle.

Does it cost him?

You've wasted a little of his time (less than you spent destroying the place), taken resources, reduced his trophy count, triggered his traps, and killed the troops in his clan castle so that new ones will have to be requested.

Aside from draining some of his resources, how else do I hurt him?

Revenge is useful in that you don't have to pay to attack, otherwise they probably aren't paying attention enough to even notice that you are doing a revenge attack. But if you are dead set on hurting them, there are 2 ways to "hurt" someone most:

1) Make sure you destroy whatever it is they have the most protected. That's what they value most.

2) Raid but don't "Win" - winning gives them a shield and protection for a time. Losing leaves them open for someone else to come in and raid them again, taking even more of their resources.