Wow...you are makin my head hurt.He shouldn't be hit in the first place. An extra 30 hp isn't gonna do much when the wizard has no AC and no DR to help things out.
(Just my opinion)
The way I see it, a good caster-wizard knows to not get hit, whether he/she 10 hp or a thousand. If the wizards you roll with are getting hit, they must suck something mighty fierce.
(A lot less opinion)
Try looking for some WF wizzys: they will self heal, and to get a WF, one much at least know a little about the game.
(Opinion again)
Toughness is useless on a wizard, unless he planned to take hits from the beginning or is going for PM[Rip on PM later everyone. This is about all of us wizards right now]. Some do. Some don't.
(Fact)
Everyone runs quest differently. On my low hp wizard, I rarely die; I know what to and not to do. When I do die, it's planned and I have already asked the cleric for a res after a certain amount of time, told the shields not to follow me and set things up to get the most from my death. Ask anyone I roll with if I drop dead constantly, because I aggro'd everything, but couldn't escape.
If you have death problems, talk to the player. If he is an idiot, kick him/get a new group. No need for anyone to gimp their build, just to die the same exact way, slightly slower.
(Reiteration/TLDR)
Toughness is useless, everything depends on how you play, work around idiots.
Simple.
I shall refer to you from now on as ... DING!