Basically, I'm looking for high-attrition RPGs on GOG that do it well. In particular, I'm looking for RPGs where you have to worry about things like this:
* Will my resources (like MP) hold out long enough to finish the dungeon or reach the next town, or should I head back to the (previous) town to rest and regroup?
* Should I cast my mega-nuke on this encounter, or should I save it in case some nasty encounter will come up later?
* Are the enemies dangerous enough for me to use that mega-nuke, or should I just take the damage and heal afterwords?
* Is it worth trying to put these enemies to sleep, so I don't have to heal as much?
* Should I use my powerful, but expensive, healing spell to ensure that the character doesn't die, or should I risk it and use a more efficient healing spell after the fight instead?

Also, worth noting that the game has to be one that can reasonably be called an RPG, and I do not want any game where a player's action gaming skill could allow them to avoid all damage.

The original Pillars of Eternity is the only one I can think of at the moment that would fit the bill on all points.

IMO the old Forgotten Realms games (such as Unlimited Adventures) do high attrition well: will my resources hold out long enough to reach the first dungeon. :-)

There's a few things that aren't satisfying about these games, or that feel wrong, from a high attrition standpoint:
* The whole "will my resources hold out long enough to reach the first dungeon" thing feels backwards. The way I see it, towns should be a safe (or safe-ish) place where you go to between expeditions to recover your resources, and dungeons should be the places where you need to manage your resources, not the other way around. (Incidentally, Ultima 1 has this same issue, where the best strategy is to go into the dungeon right away, rather than fight enemies until you're strong enough to go into the dungeon.)
* The healing situation feels unsatisfying, and doesn't lead to the meaningful trade-offs I mention in the first post. At low levels (anything up to 10), healing spells are so weak that casting them in the middle of a battle isn't worth it; there's no sense of deciding if you want to burn up a lot of magic to save a dying character. At high levels, due to the way the magic system works, you get a decent number of Heal castings, and they don't use up your non-level-6 spell slots, and the spell is so much stronger than other healing spells that the other healing spells become pointless; you don't really save resources by waiting until after the battle to heal.

Darkest Dungeon comes to mind. The resource management is incredibly tight in that game, and due to the semi random mature of everything, you can occasionally get over-matched.

Morale and sanity, as well as over all health are resources to manage there as well. I don't love the game for these reasons.

I'd say Pathfinder Wrath of the Righteous if you are OK with D&D style rules.

It has MANY options you can set for how punishing and strict the game is. So you can customize your play-though quite a lot.