I don’t remember what Vance wizards did either, I remember one beating a foe with a big spell and that ended the combat so no description of any non casting rounds of combat. But I only read one of his Dying Earth novels. Are there useful models for things to do when not casting in any of the others?
Broadly speaking, there's three types of "magic" in Dying Earth, none of which are much like any edition of D&D.
The closest equivalent are the memorized spells that were either discovered, invented, collected and/or compiled by a legendary guy named Phandal (or something like that - there might be a silent h in there somewhere) long ago. They're actually reality hacks in the form of codified instructions to entities that live on higher dimensional planes ("Overworlds") than humans do, who react to these instructions by changing the world to do...whatever that spell does. There are about 1000 of them, many of which are "lost" and forgotten, although which ones those are varies depending on where you happen to be standing at the time. There's only a few (less than a dozen) seen in use in canon and the ones that allow you kill things pretty much just do so, no saves, to chance of survival, just die. The one you're talking about is probably either Excellent Prismatic Spray (which runs one or more targets through with a kajillion magic laser beams) or (IIRC) Phandal's Gyre, which lets you grab a target and lift them into the air for an extended period, as well as imparting rotation to the victim that you can vary at will from "annoying" to "spin so fast your limbs detach" in terms of speed.
They can do almost anything in theory, but any single spell is quite inflexible (the Gyre is the only one I can recall with much choice involved beyond targeting). Worse, you can only memorize a few at a time, with dabblers and frauds like Cugel struggling to manage even one, professional magicians like Mazirian carrying a handful or so (probably less than a dozen even for the best practitioners) and archmages generally not bothering with such prosaic and unoriginal magic (more about that below). Amateurs can easily fumble the words and gestures of a spell, and interruptions could probably also cause a miscast. At best a miscast spell does nothing, but you may also get entirely different and unpredictable results, or the spell may go off more or less as normal but in an uncontrolled manner. For ex, Cugel has a spell cast one him that causes a winged demon appear and carry him off to a distant location (technically a travel spell meant to speed his journey on a quest), and when he later (barely) manages to memorize that spell he blows the casting when trying to banish an enemy, resulting in the demon carrying Cugel off instead and dumping him at the same remote location it originally did.
It's worth noting for D&D players, there's no hint of anything like "spell levels" in the books, and for all we know every spell in Phandal's codex is equally difficult to memorize regardless of what it does. There's certainly nothing like "apprentice spells" or cantrips, and the main difference between mid-tier magicians is simply the number of spells they can memorize and what spells they have access to in their libraries. Spell complexity might vary, but if so you never see a character thinking about taking more or less complex spells to optimize their loadout, much less employing upcasting or any kind of metamagic. These things are all pre-programmed codes for manipulating the universe, and not even Phandal tried to tweak them for different effects. "Vancian magic" is not a very accurate term for what D&D magic has evolved into over time, and wasn't close even in OD&D.
If you're relying on memorized spells, when you run out of useful ones during combat you have several options. Fleeing in terror is popular, as is begging for your life or attempting to arrange a ransom for yourself. The latter two are made much more difficult if you've just killed a bunch of people with the spell(s) you did have, of course. More valiant magicians might consider drawing a blade or even engaging in fisticuffs instead, with varying results. There's nothing stopping Dying Earth spellcasters from wearing armor (other than the chafing and cutting a decidedly unfashionable figure among civilized society) or learning to use a sword well (although the commitment of time and effort to such physically strenuous activity doesn't appeal to most folks). Failing all else, if you have allies in battle, any advantage your demise might provide them will no doubt be appreciated posthumously.
Because of the limitations of memorized spells, most magicians of any rank (and, indeed, most people, period) keep an eye out for exotic items and substances that can produce "magical" effects in D&D terms. These might be the result of actual enchantment, poorly understood vestiges of ancient scientific principles, a gift from supernatural entity, or even just a carefully guarded family recipe handed down for generations. Examples include Living Boots (stolen by Gygax as Boots of Striding and Springing, but alive and capable of exhausted or killed), swords that enhance their wielder's skills and cut through materials far better than they should, a wax applied to one's footwear that grants you the ability to kick an object and render it weightless for a period, flying cars, starfaring palaces, a bewildering variety of vat-grown biological constructs including ones nearly indistinguishable from human beings, and of course Ioun stones, whose exact abilities are largely unspecified but even the most potent mages lust after them. Pretty much anything is possible, with some being essentially everlasting while others might have limited uses or require some form of recharging process sooner or later.
The wealthy and powerful (a category that includes most magicians beyond mere dabblers) will have access to increasing large collections of this sort of stuff, although not all will be useful for adventuring and many may be quite useless but prestigious for their rarity and/or historical value. The poor and downtrodden will usually be on the lookout for even minor items, anxious for anything that might let them rise above their current situation in life. Outright theft (with or without violence) is frequently involved in adding to one's collection - or subtracting from another's.
Archmages are the (some would say thankfully) rare magicians who've learned the arcane process of summoning and binding a sandestin, which is a minor Overworld entity that could reasonably be thought of as a genie out of Arabian Nights, only snarkier and more prone to hair-splitting legalese and pettifogging proceduralism. They can fulfill virtually any desire of their "master" and only another sandestin or similar entity can provide much opposition. Getting them to do so is partly a matter of negotiation, and there's a poorly-defined system of "indenture points" that their services cost, with them eventually earning their freedom and the archmage needing to summon a replacement - although nothing like that ever happens in the books, nor does anyone involved seem overly concerned about it.
Thankfully, archmages spend a lot of time either living lives of luxury, dabbling in hobbies (magical or otherwise), and engaging in petty one-upmanship with their peers rather than, say, taking over the world, blowing up the already-ailing sun, or other grandiose lunacy. In short, archmages are lazy and rarely motivated to do much of import, and their sandestins are even more so.
Because of the versatility of the sandestins, archmages seem to have universally abandoned the fuss of memorizing Phandal's spells despite having access to many of them in their libraries. They do have incredible stockpiles of odd "magic" items, legions of constructed, summoned or just plain hired servants, and decades, centuries, or even millennia of experience at not dying an embarrassing and unworthy death, so even with the least cooperative sandestin they generally have quite a lot of resources to draw upon if they're somehow forced to defend themselves in combat.
