Destruction is viable. You just need a shit-ton of crit to make it not suck ass. Really though, you become a one spell wonder. As for Demonology.. until they make felguard useful, I don't particularly see the point in it considering how fast it goes down.
And after looking at your spec and gear... I'd say that you should probably scrap destruction and demo until you do some heroics and go with affliction. It's the easiest spec to do damage with and not have to dedicate yourself to seriously raiding. Your points are well into destruction, but there's a number of talents that you probably don't need. Ruin looks much better in theory than it actually performs. If I were you, I'd go with something similar to this:
http://www.wowhead.com/?talent=IVMriRfkVtbo0xZxx0z
CoA > Corruption > Siphon Life > (UA > Immolate) Drain Life or Shadowbolt depending on the situation. Unstable Affliction is a bit over rated in PVP and PVE, but it's decent enough. And the damage returns on Immolate almost always make it worth casting, despite what some locks think.
Also, one point in Shadow Embrace adds another debuff that counts towards the bonus you get for Drain Life. It's basically the only reason to have it. Though if you end up becoming a heavy raider, 5 points isn't too bad for a group... but I think there's better things to put your points in.
Another note, the Frozen Shadoweave set is excellent. It can last you well into 25-mans, and is easy to make.
http://www.spelldamage.com/Warlock/ is fairly useful. As well as other theorycraft sites. Might want to check out the mod Dr Damage as well.
But, really. If you want to stick it out with Destruction. Get your crit at least above 25% or else you're just wasting your time with the build.