I ran two games of Curse of Strahd which ended recently, and ran a much more "gritty" (for lack of a better term) game. Here's some of the things I had:
Healing Word and Cure Wounds did not exist in Barovia.
A Short Rest was 8 hours, a Long Rest was 7 days.
The '3 Death Saves' system was replaced with the Exhaustion chart, and Lingering Injuries occurred when PCs reached Exhaustion Level 4.
I did allow some "healing" to occur... players could still spend Hit Dice, the Healer feat could be taken and used, Paladins could still Lay on Hands, and Potions of Healing existed and herbalists could still create them.
The results were as follows:
A 7-day Long Rest period was too long. The actions of the PCs in both groups in Barovia could not warrant "taking a week off" from both their actions and the results of their actions. Time could not "stand still" as it were to let them regain their health because the plots and stories they got themselves involved in would not let them. As a result, I ended up having to shorten Long Rests down to about 3 days (+ a day or two if a PC was in Exhaustion Levels 4 or below) just to allow forward momentum of the story while still trying to maintain some semblance of "grittiness".
What this told me is that it would be impossible for me to ever create a "realistic" type of recovery via rest situation in D&D, unless I purposely created short adventures that allowed for Downtime between them (and thus could also lay up wounded PCs). Curse of Strahd was definitely not that kind of adventure.
It also made explicit the idea for why Hit Dice exist in 5E as well as overnight recovery. Because my players constantly talked about how if they had the Healing Word and Cure Wound spells at their disposal, they would have just cast and cast and cast them over and over to get everyone back up on their feet, then slept, woke up, and just cast and cast and cast some more if it meant they didn't want to spend 3 to 7 days "resting" for a Long Rest. Which tells me that even if I was in a future campaign to make it such that the recovery of spells and class features remained a 24 hour "long rest" but that healing and the recovery of hit dice were kept to 5 to 7 days for a "more realistic slow healing" type of situation... the players wouldn't bother waiting. They'd just cast healing spells ad infinitum. Which truth be told, is pretty much exactly how we always played in AD&D, 2E and 3E as well. Screw long natural healing recovery times... just bust out repetitive Cleric spells or Cure Light Wounds wands.
So my conclusions were that all long recovery times did was screw up adventure pacing unless I was to build a campaign specifically to have individual short adventures that could Downtime between then. Also, that any delay in recovery that could be overcome by just casting healing spells would be taken. Essentially, we'd be having Clerical 5-Minute Workdays.
My solution going forward? No idea. I ran a pair of Tyranny of Dragons games using the standard 1 hour / 8 hour Short/Long Rest mechanics (which were... fine, I guess), and a pair of Curse of Strahd games using 8 hour / 7 day (eventually 3-5 day) Short/Long Rest mechanics (which really didn't work for long rests). Neither blew me away. And thus I need to try to figure out something else.
