This answer contains annotations for the House of Death and is based on my personal experience of playing it as well as on the Curse of Strahd source itself.
First of all, a "dedicated healer" is something that is rarely seen or used in DnD 5e. The game provides insufficient support for characters who intend to heal other characters with most of their time, and the spell healing ability is usually derisory compared to the amount of damage dealt per turn. The best way to keep your friends alive is, in most cases, to help defeat their enemies quickly instead of trying to repair the damage they have suffered on the fly.
That said, healing magic or other powers like the healer feat are very helpful in saving characters from zero hp – even a single life point is enough to give them all of their actions and to prevent them from having to save death.
But Death House is not quite your average adventure. Another reminder: the ahoy spoilers.
The House of Death is extremely lethal, assuming your players make the wrong choices – yet quite reasonable -. Fighting, which is usually the most dangerous part, is actually not the worst thing: rooms filled with poisonous fog and doors transformed into blades of fake rotation will quickly carry a part at the end of their resources, unless you're extremely lucky with their Rolls. Loss of health is not easily preventable even with conservative gameplay, and rescuing unconscious characters quickly becomes a handicap without quick healing in home conditions.
To illustrate our point: our party has come in with all the resources. We had a Paladin to heal, and my monk had the healer feat and a healer kit with me. We went out with all the slots used, the complete healer kit used, with two characters at zero PV, the other two at a single VP, and that was with me and the Paladin to shoot everything we could on our respective healing resources so many would consider to hunt. Death House is mortal.
Suggestions for mitigating death
The house is not at all dangerous if your players choose the right choices. As I've already warned you about spoilers, I'll say it in advance: to prevent the house from turning against the PCs, a creature must die in the basement sanctuary. Being open about the death of adventure can push your players to make the right choice and accept the consequence of losing one of theirs. Although it is not obvious, the sacrifice does not have to be humanoid in nature: every creature will do the business. If you feel particularly merciful, give them a NPC henchman to sacrifice, after which the party can leave the house unimpeded or an animal that they can capture for this purpose.
For a less lenient alternative, you can slightly change the rules of the house. My curse of Strahd, GM, suggested that the house be appeased when a PC dies, not even in the sanctuary. This will preserve the feeling of death, but politely avoid your players the disreputable decision to sacrifice and allow them to let everyone alive. You can of course also extend players' abilities to a certain extent by giving them health potions, but this is a slightly capricious alternative: it can happen that the PC carrying the potions turns into a single point d & # 39; Failure whose unconscious condemns the whole party.
As a general rule, it is up to you and your party to decide whether this type of violence and its extent is desirable. The best you can do is warn them in advance, really, that it will not be their average heroic madness, but rather a nightmarish situation where their characters will have the chance to survive and that some PC deaths are the expected result. If you or your players prefer this heroic adventure, I suggest not to play Death House with them.