The only thing I don't like about no healer, is one member dies but the rest survive.
Which happens fairly frequently, at least for me.

My Paladin is easily the hardest toon to kill on the team.
Armor, shield, bubble, self heals -- never out of range/LoS/IWT-running off, plus the DK's can Death Grip things off of me.

Any smart opposition of course do go for the Paladin.
Melee are without a paddle and up shit creek... the DK's constantly snare them.

Casters can hit hard, but the Pally can outheal the DPS of any two casters fairly easily, at least as long as the mana lasts.
And the DK's can Death Grip a caster into their blender, which includes the Mind Freeze every 2.5 seconds.

If you can work a healer into the team, and find a way to protect them...
I'd definitely include one.