I wanted to report a potential bug I experienced. My Sorceress was instantly killed by Oblivion Knights at the Worldstone Throne, despite having over 1,200 health and no high-damage enemies nearby (such as Gloams or Stygian Dolls). This kind of one-shot death is something I’ve never encountered before, and it didn’t seem consistent with normal game mechanics.
Is there any possibility of recovering the lost gold and experience due to this issue?
Without knowing the situation: one-hit-kills happen and 1200 health won’t save you from them. Double that might.
On top of that … why care about gold or exp?
You did not play hardcore so you can get everything back over time.
Does oblivion knight do that much dmg? I know they used to cast Iron Maiden but that only works with melee characters.
Dude… not sure how much damage the oblivion knights are doing, however be aware there are oblivion knights also can Decrepify a debuff on you and +50% to physical damage done to you for all enemies or they can cast Amplify Damage a debuff and +100% ( 2x) to physical damage done to you by all enemies,
on top of this all monsters have exactly 5% chance to crit ( a.k.a do double damage)
so if oblivion knight did crit and you were Amped, this means oblivion knight did 4x his normal damage assuming you had 1200hp 1200/4= 300 , so if the oblivion knight does at least 300 normal damage or more and crits while you are Amped he can indeed oneshot you. and frankly after often comparing various mob damages on maxroll d2planner, i can comfprtly tell you that there are monsters in the game that can do over twice as much as 300 dmg in a single blow without being buffed by anything, or critting…
sorry man you just need to git gud…
On top of that as a boss group they can bring some nice aura’s like Might or Fanatism …
and if they are champ packs they can also be “extra strong” if i remember right which makes their blows even more deadly, and yet even normal oblivion knights can easily 1 shot 1200hp player… 5% chance is literally 1crit every 20 hits on average. 1200hp is a walking deadbead on hell diffculty, So better teleport out of danger with such hp than to tank blows especially from hard hitting mobs that cast amp damage. and it is especially bad idea to be a nova sorc with such a low hp unless one has 95% energy shield, but then agin he probably wouldn’t have 1200hp, unless his gear is near perfect, but if it was he wouldn’t be 1 shotted by an oblivion knight… as i said he simply needs to “git gud”…
In my experience, HC deaths of this type (with ~1K+ hit points) are usually the result of desync and / or lag – e.g. it looks like your Sorceress is miles away from the Oblivion Knights (at least it does on your PC screen), but from the POV of the server, they are right next to you and about to do a tap-dance on your head. 
The only real solution to this, given the antiquity of the netcode in D2R, is to Teleport around a lot (this forces a reset of your character’s location from the server perspective).
Unfortunately… not even this, works 100% of the time.
This is a game from 2000, after all.
or buy a routing service, that will shorten and optimize the routing between your ISP and the game server, possibly eliminating the problematic spots