Andor's Trail

Algrangor confessed her evil plan to me, after I placed the 5 idols. I returned to Remguard; everyone is still alive, but sick. Is there any way to either remove/destroy the 5 idols ( they're still by the beds) or Heal/Warn the victims?

No you can't

May wearing Algrangor's necklace ever reminds you to have a bad conscience

Congrats! You now own the best necklace in the game and one of the best items period.

The people she targeted are still alive at the moment, and the idols are still by the beds. Those 2 facts, alone, are reasons to have this be the start of a new Quest, for penance & forgiveness.
( for the 5 rats/people I unwittingly killed. )
Still another branching Quest possibility is :
( assuming the people could be saved.)
Algangror discovers your betrayal ( to her ) and starts a campaign against you, cursing the "Marrowtaint" necklace, preventing you from removing it, giving detrimental effects, as well as being a homing target for evil Deathstalker monsters trying to track you down and kill you.
( Think, soulless black, ghost-like wraiths with red eyes, able to go through the walls of buildings, able to go directly through the normally impossible terrain features, like trees and rocks ( but not able to cross running water, except over the nearest bridge.)
Their dark energy would have a 5% chance to utterly destroy ANY weapon used against them, and a 2% chance of destroying a random piece of a character's armor with each successful attack. They wouldn't need high hit points, but 5-7 of them would slowly/randomly track along behind/toward the player character, across the different maps. Being undead, they should be slower than player characters;
( maybe a 6-9 ap? with a 3 for attack, and a 3 for movement ), but, they would be able to go THROUGH all the terrain features a player character would have to go around. They should also gain perhaps 60ap of travel, every time a player rests. ( and you should be able to see them as black shapes when you call up maps, just to instill dread in the players) Certain sensitive NPCs should be able to either see, or sense, these Deathstalkers following the cursed player; this would allow for terrifying dialogue exchanges with the character ( increasing the dread ) Perhaps other npcs would start to shun the cursed character, out of fear of being the next target. Resolving the Quest(s) to free yourself from the curse, should involve multiple long trips across the continent, giving the Deathstalkers time to grow in numbers and power. Players will laugh off the undead shadowing them, until the first time they PERMANENTLY lose a precious weapon or item. What do you think?

"slowly/randomly track along behind/toward the player character, across the different maps"

The game engine doesn't support this. Within a given map? Yes. Across multiple maps? No.

What if it auto-generated some from the direction the player entered each map? ( after a brief delay) that would give the impression of being followed?

Interesting idea, but as Antison says, the game engine does not support what you suggest.

Let's assume we could change the engine for it - what of it can be realized?

1. A cursed item:
Worn items could have a cursed attribute, something like a condition, that wears off after some time or by sleeping. Or everlasting (like the rotworm).
This curse counter starts at the moment you put the item on. Or it starts with a reward from a dialogue script. It can also restart or end with a script reward.

This would be a nice enhancement that we could use in various places.

2. Following
It was very much work to make Gyra in Stoutford follow you in a certain area. But the automatic spawn of an NPC after some time could work. I see the following difficulties:
- if you change a map and just stay still, the follower shouldn't spawn. He should spawn a certain time after you have moved from the map entry.
- maybe the follower shouldn't follow into houses, because these maps are too small with only 1 exit normally. The follower only enters maps that are on any worldmap, this could do the trick.
- walking anywhere just is not possible without reworking most maps, so absolutely no to this.
- Every actual NPC is defined as part of its map, has a spawn area and is saved with the map in the savegame.
Autogenerated NPC would be totally different. If they were not saved, then a simple save/reload would let them vanish. I don't know if the engine can be changed to let you interact with NPC that are not defined with the map.

So Following would be rather much work, if possible at all although it would be nice.

3. Broken items
This would be doable but we don't want it. In fact we had discussed this years ago already, but put it down as too harsh.

1 and 2 might be possible, but some amount of work.
We have no capacities to realize this, it would have to be done by someone of our community.

I appreciate the detailed answer, it's so much better than the sparky answers. What do you think of my original suggestion, of a new quest to try to save the townspeople before they die? It could be long and involved, gathering different substances to heal/cure them, or short, like asking the town's Cleric to use a ritual to destroy Marrowtaint and it's curse? ( and, of course the repercussions of that with the Witch...)