My experience of 4E was that healing was something each character could manage pretty well by themselves - no real need for leader-type characters.
That's intentional. There's no hard need in 4E for any single role. A balanced party will outperform an unbalanced one, given equal player skill and cooperation, but not by such a huge margin that it's unreasonable - this is precisely why we were confused by Ahnehnois' piece about how roles should be balanced with each other - in 4E, they largely are - if you lose a Leader and replace him with a Striker, the greater speed at which enemies fall will help to make up for the shortfall in healing. My main group is missing a controller (most of the time) and has a second leader, for example, and works very well.
There are places where certain roles shine, of course - unavoidable damage or really lengthy fights tend to benefit from a leader, swarms and large numbers of minions are harder to deal with without controller, and so on.
But
if you believe leaders are any less essential than other roles (and I'm not saying you do!), then I think you are quite mistaken.
On this we can definitely agree. As a GM, my favorite aspect of play is having my players' PCs fail at an objective that is thematically impactful to them and watching what comes out of it; seeing how their characters' ethos, outlook, relationships (with people, places, things) and/or goals evolve (or devolve perhaps) as a result of the fallout of the failure/loss. How it might put them at tension with their former selves or at tension with one another.
Failure is certainly potentially interesting.
Failure
because no-one decided to play a specific class/role, on the other hand, is absolutely the least interesting kind of failure (far less interesting than "bad rolls", even!), and may even put people off the game system entirely. It says more about the DM (in a more linear, story-centric campaign) and his encounter design, or the system (if certain scenarios require a certain class, even if more "real" logic doesn't dictate that they should), or occasionally the ability of the players to handle logistics, than it does about the characters or the like.
I know that I've seen failures in RPGs before that were solely related to this kind of thing - i.e. "We didn't have X class with us, so we failed" (8/10 X is a Cleric or very similar class), and the results were never character development or the like - they were universally disenchantment with a particular system, or recriminations between players (not characters).