I'd say at least 6th level for Wiz/Sor. It's a pretty big thing for Clerics (and Druids) that they are the masters over things life... especially regarding healing. It's the tradeoff they accept for not (in theory, all Cleric imbalance arguments aside) being blasters.
Furthermore, I'd say for a Cleric to cast this (and I see absolutely no reason why this wouldn't be on the Cleric spell list) would be at least 6th level, since it also includes a save or die affect. Which in general means that Raise Dead is simply a better option for a Cleric. Alternatively, I'd simply tweak Raise Dead to substitute a human life for the diamond, which would in turn make Raise Dead and [Evil] spell. Finally, I wouldn't let Druids cast the spell, for purely flavor reasons... it's completely against the cycle of nature.
Given this, I'd place this at 7th level for Wiz/Sor if this is a seperate spell, or 6th if you simply tweak Raise Dead.