It's amazing how many people equate "healer" with "hit point regain bot". Beyond level 4 or so, the real danger isn't lack of hit points but lingering status effects. Blindness is a 2nd level spell and is a lot more effective at taking people out of the fight than a sword trust or hammer blow. The same goes for curses, stat drain, paralysis, diseases, fatigue, and the eternal problem fear effects. There's plenty more I could add, but you get the picture. One aoe fear spell has a much bigger chance at inflicting a TPK than all the fireballs in the world at the same CR - and no amount of magic items you think to buy with your cash will cover all the possible status effects, drains, etc. Especially when you are far from shopping and hirelings, a party cleric/oracle/etc is critical.
