'Framer' if you think about it staying longer in that hold (assuming yr stated conditions re fuel) then regardless of any regs you obviously can't remain in that hold beyond 10 mins unless of course you desire to land with less than the legal fuel reserves & if that be the case then you better have a good reason for doing so:-)
.............hey 'W9' there is one major consideration that will stop you from holding as long as you like, it's called fuel!!
I am not aware of any reg's as such (there's plenty of Reg knowing pilots in here whom maybe able to quote) that state the things yr asking as it kinda doesn't make sense, you either have the fuel to hold 'till next week or you don't & in yr above mythical scenario you don't:-) You can obviously enter the hold as ATC have instructed but after 10 mins it's all over in yr case.
The only time you can stay longer in that hold & use yr Alt reserves is when you know from a legal standpoint & a common sense standpoint for that matter is that the wx at yr original destination is now at or above yr Ldg's req's now known from say an updated TTF.
This happens quite a lot when on say a ML-PH run when fog is about & you continue along yr route updating TTF's as you go to make sure yr not going to get caught at the end of the flight in less than the min req's.
Of course all this is very subjective as the wx-man is not a guaranteed source of exact science resulting as I mentioned earlier the recent MIA Ldg's by the 'big boys' but we do our best with what we have:-)
So I guess to answer yr Q as diectly as possible (What piece of reg allows you to stay longer in the hold) that reg would be a TTF for Eg that says the Ldg min is now at or above yr req's & yr original Alt fuel suddenly becomes holding fuel in yr case:-)
Back to the word 'committed' which seems to be the fly in the ointment here we are all 'committed' at some point in any flight based on the gas we have in the tanks, unless of course the ice is running out for the first class pax's drinks
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Regs or no regs the basics of any flt is to leave the ground for yr destination with the fuel req'd to cover all contingencies based on the wx at the time of arrival (Alt's inc). Anything that changes en-route will obviously be deal with on a case by case basis.
Wmk2