Assuming your mage has around 700 hp, nothing big, though it means your drow needs to be loaded with at least 2 or 3 pieces of high quality HP gear that are most certainly going to disappear when he dies. Still 700 HP is a reasonable number.

Without any outstanding extra protections (stone skin, prot vs. align/element/metals) I think shield and aura at the very least are necessary to compete, especially with Landslide remaining as popular as it is. Conjurers need time for their servitors to get their thumbs out of their asses, shapeshifters that tank with their faces aren't going to outdamage a warrior or assassin, and transmuters are nigh useless using their innate dam redux if it means they can be tripped to death. (though I still don't think malleability was ever necessary to add to the class, it's what makes the higher level battles against neuro anywhere from painful to hopeless if you aren't geared in top quality saves gear and can't parry staff)

Now, of course, that's only talking about normal 1v1 pk. For cabal raiding, unless you bring overwhelming force, you need all three, and if you're solo it probably still isn't going to cut it against certain inners (read: Primeval Spirit, Watcher and Nexan inners) without regen.

If your HP total goes up or down, the need for all three changes (with mages sporting 1k or more HP having the margin for error and RNG to forego aura, and newbie mages sporting 500ish or less HP with around +100 in HP gear have a definite need for all three plus a well thought out plan)

Mages sporting 1k+ HP using shield and aura are hard to kill. Unprepped warriors or your run of the mill bard are not, unless you forgot your resist mental prep and got distorted, which is a different balance discussion altogether.

Having had Kasir remove 33% of that 40%ish dam redux using silver malison, it is indeed important and necessary. Otherwise don't bother ranking beyond 40 and don't kid yourself about ever killing any leader chars, paladins, druids and shifters with high mobility, to say nothing of giant sword warrior.