I would like to suggest that Fighter's death protection stack with other forms of death protection, so that a Fighter who found a CYDSTEP glyph would be able to have two levels of death protection at once. The CYDSTEP protection would work as normal; the Fighter death protection would activate only after CYDSTEP was used up (and not cast again). I make this suggestion because I like Fighters, and think that although they are a great class at the start of the game they need a little bit of a boost later on.
Fighters are perfect as an introductory class, making things go smoothly for players who are still working out the various tricks to conserve resources and get bonus experience. When you're just starting out that layer of death protection is both useful as it can be an important source of bonus experience or part of a boss-slaying strategy, and reassuring in case you make a mistake or need just a little bit more damage to finish off the boss. It also just sounds really cool; a Fighter can take a hit that would kill any other class.
But then you unlock CYDSTEP. Now one of their attributes - the only one that isn't purely about leveling up - is completely obsolete. Even at the very start of a new dungeon a Warlord has better death protection than a Fighter - the former can cast CYDSTEP right away to get the same effect, and not only does the Fighter typically not have anything to do with his own mana, the Warlord can regenerate with just a couple of steps and have a second layer of death protection ready to cast, giving him an additional attack (with +30% damage as well). There is no other class ability that can be so completely replaced by a mere glyph - yes, there is a first strike glyph, but Rogues and Assassins have first strike for free and never lose it; yes, there is an attack bonus glyph, but it stacks with class attack bonuses; yes, there is a healing glyph, but it stacks with healing potions. Even the Fighters' other abilities are supplemented by their analogues, e.g., the bonus experience stacks with Tikki Tooki's bonus experience boon. The Fighter's death protection is the only ability the game that can be made completely obsolete.
The fact that CYDSTEP can randomly spawn in dungeons puts Fighters in an awkward situation. Early on in a dungeon, it is very likely that you'll encounter a higher level monster that you could beat if you were to use your death protection on it - but if you want to conserve your death protection, you'll have to give up on that bonus experience or continue to explore. Without taking CYDSTEP into consideration, the player has to make a tactical choice between immediate benefit now versus saving that benefit for later use against the boss. However, the possibility that CYDSTEP was spawned in this dungeon complicates things. If you save your death protection until you find the glyph, then you got almost no benefit out of it. Any class that finds CYDSTEP has the exact same benefit as a Fighter, essentially meaning that one third of the Fighter's abilities was not used in that dungeon. Yet if you use the death protection early on with the expectation that you'll be able to find CYDSTEP later, well, it might not have been spawned this time.
Thus, when faced with a choice to use up death protection now or save it for later, you are essentially making a random guess as to whether or not CYDSTEP has spawned. There's no way to know whether or not you'll find it, and if your guess is wrong then you have potentially wasted a significant resource.
I think this dilemma could be solved by having Fighters' death protection be tracked separately from other sources of death protection - i.e., as a separate player status that can be active at the same time as CYDSTEP death protection, and which is only triggered if there is no other death protection active. So a Fighter who casts CYDSTEP would have two death protection icons - if he took a deathblow, the CYDSTEP protection would be used up and could then be re-cast if he had enough mana. Only if he took a deathblow with no other death protection active would his class-based protection be used up. (Although I refer only to CYDSTEP, I think other sources of death protection - at the moment, Taurog's boons and the consumable item - would continue to be treated as the same as CYDSTEP. Namtar's ward, on the other hand, I would suggest be treated like the Fighter's death protection; partially because otherwise it's currently nearly useless if you have CYDSTEP, because it currently fits so well with Fighters if you don't have CYDSTEP, and as an expensive and rare preparation it should have a bit more oomph to it, in my opinion.)
This would restore to the player that pure tactical choice - use my death protection now to level up, or save it for the boss - without having to guess as to whether the glyph has spawned. It would keep Fighters pretty much the same early on, but give them a little bit of a boost as the dungeons start getting harder, which they could probably use.