Look at his reference picture and then think of his arm's position, his neck isn't that free a target. Not to mention if Gigue gets into that position drawing a knife to strike seems like a massive waste of time, he could just punch Sigurd in the face in half the time and knock him out. Your character's strength is actually insane, giving him the benefit of the doubt in regards to his punching form he can generate more force with his punch than any living human at least twice over, Sigurd isn't a boxer (trained to take punches to the face) and even giving -him- the benefit of the doubt he'd still be debilitated by a single punch. Why waste time with drawing a knife?
That being said, Gigue is already an unstoppable badass, multiple rending wounds, badly injured arms and even broken ribs and he's still performing acrobatics and break dancing, what more can Sigurd do?
Well, strength does not always equal to punching force. In Gigue's case, he punches just as your normal heavyweight, since it is stated in his CS that he is just as fast as any other human martial artist, meaning that in accordance to the formula of kinetic energy, he doesn't gain that much of an increase in power. Sure, he is slightly less impeded by the inertia of his own bodyweight and has a pair of shiny brass knuckles, but i think that is a negligible advantage in comparison to the penetrative power of a knife stab.
The only things he can do better by virtue of strength is grapple and throw around heavy objects - and as mentioned prior, his own body included. For that reason, i decided that with both legs and his lower torso intact, it wouldn't be unreasonable to have him do the flip kick as a desperation move, in order to make sure Sigurd wouldn't be slipping out of his reach anytime again. The guy's been fighting for the better part of his life with fists alone, so it'd be safe to say this isn't his first time pounding an enemy into submission while hanging on by the skin of his teeth.
Certainly, i have not emphasized his tiredness that much - but having both limbs on his left side be useless is quite debilitating on its own, and as i have said in my IC post, unless Gigue wins this skirmish, chances are, he's done for.
EDIT: that being said, i really did want to follow up Gigue's ass slam with the dreaded crunch punch.