Our group plays with out a Leader. We have five players (Paladin, Warlock, Rogue, Ranger, Wizard). Two players are veterans, one has played 2-3 campaigns before, and the last two are first-timers. Never played any RPG at all.
Here is how it plays out:
1) Healing Potions have become very very useful.
2) The Paladin concentrates very highly on defense and drawing attacks to himself. His Lay on Hands is usually placed on himself, but he tries to save it as long as possible for characters that may be out of surges.
3) Battles are bloody and hard-won. Everyone is low or out of healing surges by the end of the adventure.
4) We are playing through the Scales of War adventure path, with only stylistic changes to the encounters. The effectiveness of the enemies remains the same.
5) The Warlock is played as a combo Striker/Controller, and the Wizard is played more as an AOE Striker than anything.
6) The Paladin's ability choices tend to be towards abilities that grant defense or healing. His damage output is very minimal. He just tries to stay alive and keep the bad guys off his allies. He is considering multi-classing into Warlord for some extra healing because there are battles where it would be needed.
7) The combination of (essentially) 1 Defender and 4 Strikers is pretty devastating. Enemies are not in play for very long before this group can take them down.
8) In the interest of full disclosure, they have had one death. The Paladin died in the Siege of Bordrin's Watch in the room where they save the dwarf paladin. But it was more due to bad rolls than anything...he had about 2/3 of his surges remaining when he died.
So what I've learned is that it's definitely do-able. Having two veteran players to keep the group's tactics strong is a huge plus. This group works like a well-oiled machine. They are constantly working towards flanking, guiding enemies into clusters for AOE's, taking heat off the paladin when he's in over his head, etc.
We've played D&D (I and the two veteran players) since 1st edition and have never had a truly successful group w/o a cleric or other healer. This is the first group that is viable w/o a cleric. Are the battles tougher? Absolutely. But they are perfectly able to pull it off so far, and I haven't had to pull any punches whatsoever.
El Cucuy