Ancalagon
Dusty Dragon
A very good point.Since it's an NPC give him a Shield Guardian. That effectively doubles his hit points.
A wizard would have some kind of body guard... a few skeletons, some form of construct, a fiend... memorizing a summoning spell, especially if it's a creature that has useful non combat applications is another good idea.
I think it really depends where this wizard is though. Are they in a busy city? A court mage? Lonely tower on the moor?
That being said, I think that the OP's question is very valid. And I think that a wise wizard would have, at the very least, a way to escape combat, as many pointed out. And those emergency scrolls are... really important.