Re: Lethality - I've started running the Dragon Emperor campaign, and after about a half dozen sessions, there have been a couple of close calls, but no actual deaths.
I think this is mainly due to the Death Saves mechanic (practically identical to D&D 5E), so going down doesn't mean you're automatically dead. In fact, there's an additional mechanic - Rally - that lets a character continue to take actions even when they're at zero HP and making Death Saves. The healer in the party managed to rally themself, which is difficult to do (usually it takes another PC taking an action to say "Get back on your feet, soldier!" or something similar and making a roll.)
Having a character with healing magic is somewhat helpful, but it's only slightly better than someone with a healing skill (and bandages) when it comes to bringing a character back from zero.
BUT.... due to lower HP and higher damage from weapons (compared to D&D), a random critical could take a PC down in one hit. Damage that takes you to negative HP are also instantly lethal, no Death Saves. Some of the bigger monsters could potentially do that much damage even without a crit.
The main thing to avoid death is to play smart. My group convinced a giant to team up with them against another group rather than fight him. (Then they got to see the damage the giant could dish out, confirming they took the right approach.)
In the published Adventure, Secret of the Dragon Emperor, many adventure sites have multiple factions with conflicting goals, and players should take advantage of this, either teaming up with one against another (possibly double crossing them), or get them to fight each other and deal with the weakened survivors. It's definitely not a "combat solves everything" game. (In fact, resolving a conflict without violence is one way to earn the opportunity to advance a skill.) I definitely recommend setting up home-grown adventures with factions in play, at least some of the time.
As far as tweaking the game, I agree with some of the other comments, especially with regard to extra Heroic Abilities (HAs) at the start. There are a couple that allow you to both Defend or Attack (it's usually one or the other without this ability) that can be real game changers. I've seen recommendations of just allowing the HA Fancy Footwork (which lets you Dodge as a defense without using your action) to everyone at the start. (Note HAs usually cost Willpower, which is a limited resource)
Also, you could disregard the Instant Death rule, or make the Death Saves with a Bane (Disadvantage) if they take that much damage. Maybe even just reduce damage die of monsters and even NPCs a step. That'll usually reduce damage by a couple points each hit.