The main argument against disassembling Vanguard is what it would build into. Namely:
* Stout Shield: Utterly useless, unless your idea of an awesome late-game item is a Poor Man's Shield.
* Ring of Health: Used for Pipe, Battlefury, Bloodstone, Linkens, and Refresher.
* Vitality Booster: Used for Atos, Heart, and Bloodstone.
Bloodstone uses both expensive components, but is primarily built on ranged heroes (Storm, Leshrac, etc) who wouldn't benefit much from Vanguard. The scariest item is Battlefury, which might lead to Anti-Mage and other BF-based carries building Vanguard for early survivability. AM often picks up the RoH in lane anyways, so grabbing the Vit Booster early for nigh-invulnerability wouldn't be a stretch. It's a similar problem with Linkens carries (though many of them are ranged). By contrast, Atos and Pipe are uncommon pickups.
Basically, a disassemblable Vanguard would significantly help hard carries with weak early-to-mid-game presence, giving them an intermediary item that builds into a powerful late-game tool(s) they were already planning to grab. By contrast, few mid-game heroes (AKA the heroes Vanguard is supposed to help) would gain any benefit at all from disassembling Vanguard, as almost no useful midgame items contain a recovered Vanguard component.
If you want to make Vanguard viable in its current niche, as a useful item for mid-game carries with durability problems, buff its stats to make it a viable competitor to Drums and similar items. Disassembly won't achieve what people seem to think it would achieve.