Greetings!
Wow! Elder-Basilisk my friend, you said pretty much exactly what I was thinking!

I agree fully.
That said, on the occasions that I have encountered DM's that get a kick out of scenarios such as this, I can't help it--there's this sick, vicious, sarcastic side of me that wants to say, "Oh yeah? How 'bout this!" and proceed to just hammer the evil sorcerer to the floor. Then, take my dead wife's hair, and begin to strangle him with it. Then, roaring with rage, grab his stupid broken body, and leap fully into the demon pit, screaming in maniacal rage all the way down! My child dies, my wife dies, the sorcerer dies. Demonic hell is unleashed, and my paladin dies gloriously. Or, if he survives, he becomes and evil vicious bastard that proceeds to unleash his own hell of rape and slaughter upon the world! Yea!
Either my character triumphs in such a scenario, or turns into an evil bastard, or dies a glorious death. It seems a likely enough way to get that paladin out of the way, and roll up a new character. And yes, I'd roll up a new paladin. I wouldn't marry anyone, and I would retire my parents to an isolated monastery somewhere, and I would play a mentally-deficient paladin that only has the thinnest grasp on morality, who just likes to hack the evil things apart.
After all, isn't this what the DM wants to really happen?
I get so tired of all the DM's who hate paladins. They go well beyond any reasonable way to inject dramatic elements into the game, and instead assidiously work painstakingly to create the ultimate no-win moral dilemma for the paladin character.
Kill 'em all, and let god sort 'em out!
It makes me want to laugh in some ways, heh?
Realistically, what is there for the paladin to do in such a situation? You leap to try and save the child, and then proceed to kill the sorcerer in order to stop the gate from opening. The wife is pretty much dead, and the gate might open anyways. Then, as Elder-Basilisk said, you get to get all those experience points for fighting hordes of demons! It seems to be a no-win situation to me. The paladin can't realistically be expected to do three things at once, all in one round. He can only do so much.
Semper Fidelis,
SHARK