Bad plan, wizards are usually very squishy.

Good plan, the wizard makes a better shield/weapon when they stop squirming (aka die)

Wouldn't carrying an actual shield be easier and be more durable?

I'm sorry, is this some NPC thing I'm too Barbarian to understand?

Probably.

Wizard: I shall also wear armour. Fantasy lore: no, you can't wear that. Wizard: why? I'm going to be fighting too. I don't want to get stabbed by the first guy I see and die. Fantasy lore: no, it wouldn't be fair on the giant dragon or the deamons I'm sending you to fight. Sorry.

Ponder the blue ~~orb~~ balls

Check his pockets, he might have a phylactery.

A fun thing people often forget about Mage Armor is that you can cast it on other people, which is occasionally even helpful!

That's why my oblivion play through is a wizard with a shield and heavy armor.