My fav class/background is DEWz
I can make it through lair without a second spell book. The secret is conjur flame!!
Used correctly, spiny frogs, hydrae, orc warriors/knights can all be taken down by magic dart. Ring or staff of magic power is your greatest asset for that strategy, as anything that won't step in the flame (orc warrior, ogre, poisony things) will take up to 20 mDarts. Even grinder is no trouble for me at xl3 on D:2 with this strategy...
Also, I never memorize call imp (worthless and boring playstyle)
I train +spellcasting and *conjurations until conj flame and meph coud have no spell hunger. Then switch to translocations and charms to get blink and rmissles to 3%. then back to conjurations until meph and flame are 3%. then, if i find a buckler, get shields to 5.0... if not, train dodging or traps until my second spell book. later, get chosen nukes castable with little or no hunger (depending on your food situation... I'll keep spellcasting low if I have amulet of gourmand or similar)
I always choose sif if reasonably available, even though i'm a nuker... channeling and access to high level support magic earlier is, imo, better than lvl 4 conj spells before lair. If i find/get gifted controlled blink before good nukes, then I will stop everything and train translocations until it's reliable (cBlink is the most powerful spell in the game, imo)
Ironically, I can't get a melee char past D:6, but I have no prob escaping with 5+ runes as a Wz...
other things to note... elven leather armor doesn't hurt DE casting success (10+ AC on a DEWz by lair is godmode [through rings and weapon of protection, enchant armor scrolls, or ice magic buffs if found] - this will allow you to sustain 2-3 turns next to a hydra while he stands in a cloud of flame) later, you should get a steam dragon hide and enchant to +5... or light randart armor with some skill levels, thuogh, i think that 27 in armor will only drop -1 EV to -.3333 EV, so I think that any armor past elf leather or steam dragon is going to hurt your casting forever. that is, if you want ice storm and shatter and LCS at 1%...
other things to note for later... vault:5(8) opening is a joke with high earth magic and shatter
only train poison if you find poison arrow (super strong, but arguably not worth it... iron shot and LCS aren't that far behind in damage, and both are irresistable)
always have a backup if your main conj attack can be resisted... IMB is mega powerfull if you go glass cannon and keep conj training through lair... maybe 3 to kill a hydra, and only 4-5 for a demonic crawler (so scary)
a post lair caster feels mighty indestructable, but you will meet something called a ghost moth at some point... lol... or their evil overlord... Mennas... and unseen horrors can be an untimely death without sInv or a corridor to shoot blind in... once those 3 are no problem, you'll be ready to clear the dungeon and all early branches... then get your lvl9 storm spell castable and head to abyss for the rune... then troll through pan 3xing ice/fire storm on pan lords until you have all artefact equipment... then take slime (or earlier with cloak of preservation)... then hells and tomb if you're badass... no need to switch gods... especially if you get the necronomicon and can cast necromutation...no hunger channelin is game breaking for a caster... never did a ziggurat though, not sure if it's enough with the 1 turn loss to channel... maybe TSO or Vehumet is the best there for MP management... All of your YASD's will be a result of not running away while you still have lots of MP... remember to keep at least 2 for a blink
If your goal is 3 runes, I would go Ice Magic and take ice storm into Zot... orbs of fire will eat you alive otherwise at that XL...
tl;dr... i know... but to answer your question, change to Wz and use the support spells in the starting book to survive longer... and did i mention conjur flame?!?!?!?