Perhaps, but that would involve a bit more rigamarole than I'd like to bother with at first.
Mordor isn't a roguelike. There is some RNG, but the dungeons are set in (pardon the pun) stone. That would involve me having Windows 3.1 and the lowest I can get is 95.
Nope, Shareware. (Also part of the issue.)

Getting 3.1 is fairly easy... Especially as a pre-installed ready-to-run kind of way, just takes a tiny bit of tinkering to get other stuff working on it.

Dwarf Fortress has an adventure mode. Would it scratch some of the Mordor itch?

DF is much more roguelike than Mordor. And while gritty, there's a certain element not there.

As far as I know, pretty much all major post-3.x editions of Windows up through XP could run most 3.x software with little to no trouble (unless there were additional components that weren't supported -- which is probably not the case for this game). I know I was finally able to beat Castle of the Winds (which, as has been mentioned, is another Windows 3.x game) on an XP machine. Windows 95 would be fine for running that game (though, honestly, just using Linux + Wine on an existing modern system would probably be no more difficult than acquiring and setting up a legacy PC and OS, and would definitely be cheaper).

Perhaps. We have a legacy PC, but again I'm looking for something like it, not something that is directly it.

I said it's closer to a roguelike. The gameplay reminds me more of roguelikes than most other CRPGs.

Hmmm i wouldn't qualify it as a rogue-like... Usually rogue-likes are a single person party, while Mordor lets you have 4-6. Second if you die you can get resurrected (although there's a percentage chance which may spell doom for you). Third rogue-likes usually have far more RNG for the maps, while Mordor has 15 levels or so premade and generated, and don't change with playthroughs.

No Mordor is closer to a D&D game that isn't officially WotC or TSR.

Since an equivalent replacement may be hard to find, maybe you can share with us what are the features that you value the most. You may possibly find them in other games.

Probably impossible, seeing as it doesn't run on 64-bit systems.

Well, in no particular order, the presentation, the guilds, death was more than a slap on the wrist; but typically wasn't an instant game over, the library so you can keep track of personal discoveries, and the overall gritty AV.

There was a cloning project/remake in the works by the community, but that died back in the XP days, if I recall.

Elminage Gothic has some of those traits. In particular, resurrection can fail (and causes aging when successful), and the game has an Item/Monster Encyclopedia that is filled up as you discover things. (It is very much like classic Wizardry games.) There is, interestingly, a penalty for reloading a mid-dungeon save; time will pass, and if you do it too much (especially in post-game dungeons), your characters will age.

The reviews seem to be mixed; Mordor did slap you around but it wasn't brutal.

Here are some details on how brutal Elminage Gothic actually is. Of note is that the game starts out easy and gets harder as you progress.

First dungeon: 3 floors (all mandatory). The enemies are really easy, with none being able to do anything particularly nasty, especially if you have Song of Healing and/or Turn Recovery. The only exception is the Floor Master, who can be easily avoided (and is visible on the automap) and is not meant to be fought at that point.

Second dungeon: 4 floors, only 1 required. One enemy has a 5% chance of beheading on attack.

Third dungeon: 5 floors, only 1 required (though it's worth exploring the first basement). The only notable danger on the required floor IIRC is an enemy that can attack the back row. There's an enemy on other floors with a 20% behead rate. (Wouldn't it be nice if you could get that? Turns out you can with the help of a Summoner (ideally with Spirit Pact).)

Fourth dungeon: 3 floors (both mandatory). I don't remember it being too hard. There's some trickery involved in mapping these levels, however.

It is only after these dungeons that you start to encounter level draining, but you can quickly reach deep enough in the 5th dungeon to power level. This is also when the game starts throwing optional dungeons at you; exploring them is a good way to get experience and treasure, and the start of those dungeons isn't that dangerous.

The most dangerous enemies tend to appear at the bottom floors of optional dungeons, which can be saved until later, and in the final bonus dungeon, by which point you have already explored 70+ dungeon levels.

Of note, as brutal as some of the enemies are, the only time I have been wiped on the surprise round is when an enemy casts Miracle and it decides to teleport the party into solid rock, which is fortunately incredibly rare (and you can reload a save if you are unlucky enough for that to happen).

That does not seem easy to replace. I can mention Blades of Exile, that seems to be free now. But really I have nothing that is a good match for you, sadly.
It does seem to be a nice game, though.