It was an unwritten rule in the mercenary world that in the event of a surprise attack, the first priority of a physical melee professional was to protect the spellcaster first.
This was an ironclad rule, one that the mercenary world had taken hundreds, thousands of years to learn, a lesson paid for in blood.
Physical professions only had two functions: kill or protect. But spellcasters were different; as long as they were prepared, they could not only do the first two, but also heal, alter terrain, alter climate, control enemies, or summon creatures as reinforcements.
Even if you were surrounded and in danger, as long as the spellcaster was still alive and able to cast spells, there was a possibility of turning the tables. On the other hand, if your own spellcaster was dead, or if you had no spellcaster but the other side did, it was just as dangerous as long if you didn't have tremendous advantage in numbers.