I ran the latest packet, using the Caves of Chaos playtest, and didn't manage to kill anyone. The players cleared the goblin caves, the ogre cave, and the kobold caves, over a period of 3 adventuring "days" (2 long rests). There were 5 characters, all 1st level-dwarf fighter, halfling rogue, half elf cleric, human bard, and elven mage. I only pulled a punch once, after rolling the third crit on the fighter, and I dropped it to a regular attack. But crits can happen to anyone.
At various times, the fighter, the mage, and the rogue dropped to 0 and were making death rolls, but quick action by the cleric was able to save them.
BTW, kobolds and giant rats were scary, thanks to their pack attack ability. The goblin stealth never really got a work out because the players were able to attack by surprise most of the time.
All in all, it felt dangerous, but survivable with good play, the way I think D&D should. Assuming you're using the right monsters for the level, I think the game is pretty survivable.