OK, to my thinking you are the point where the DM is responsible. There are better systems and worse systems. But this is easy to manage and trying to remove the DM from the equation does more harm than good.
It is viable.
Who said anything about removing the DM?
However, the game mechanics should flow smoothly regardless of DM.
Players have been TPKed in the Starter Set already. There are stories about this. Why? Because at low level, it's easy for the combat to get out of control. Especially if the DM plays the NPCs smart. For example, Goblins come in, damage a PC, disengage, and go back into the woods and hide, all in one round. Or, Gobilns shoot from hiding with advantage, then move away further in the woods and hide, all in one round.
http://www.reddit.com/r/DnD/comments/29xxin/5e_the_lost_mines_of_phandelver_is_no_joke/
Sure, the DM could hide all of his rolls and when he criticals the Cleric, he could say "Ah, the wee goblin misses.". But, there are DMs who prefer to roll out in public. Even with the DM in control, the combat can with just two or three sets of rolls, quickly get out of hand.
And do you want the DM to go *Oh shoot, these guys are going to die. Three are down and two more are a hit away and I still have four goblins. Guess I'd better have the goblins yell for them to surrender.*?
Personally, I would prefer if the default game was not quite so variable at low level and allowed there to be simple tweaks for DMs who want it to be more variable or less variable.
Healing seems to be a bit of a weakness. Not quite as bad as 1E, 2E, or 3E, but still a bit problematic.