Some items can indeed be disassembled to their base components in DOTA 2. The only way I know to disassemble an item is to right click the item and a list of options will appear one of which is "Disassemble" (if that item can not be disassembled this option wont appear). When you select this option the base components will be dropped to the ground so be careful where you do this.
These items can currently be disassembled:
Ring of Basilius => Sage's Mask, Ring of Protection
Ring of Aquila => Wraith Band Ring of Basilius
Perserverance => Ring of Health Void Stone
Sange and Yasha => Sange, Yasha
Ethereal Blade => EagleSong, Ghost Scepter
Mjollnir => Hyperstone, Maelstrom, recipe
Arcane Boots => Boots of Speed, Energy Booster
Helm of the Dominator => Helm of Iron Will, Morbid Mask
Shiva's Guard => Mystic Staff, Platemail, recipe
Manta Style => Ultimate Orb, Yasha, recipe
Abyssal Blade => Sacred Relic, Skull Basher
List found here: http://dota2.gamepedia.com/Disassemble
The first blood update coming September 23 will allow all items to be disassembled within 10 seconds of making that item. In addition, items which can be disassembled say so in their tool-tip as of this update.
http://www.dota2.com/firstblood (under GAMEPLAY)