the missing pump from the main fuel tank is inventoried along with the columbia's untested exploding bolt covers and lee harvey oswald's curtain rods 'prop shop' sniper scope inside 'the largest ball of string' museum somewhere on the eye-40.
it reportedly took an extra effort by eod to make a similar main tank explode when that theory was tested. you're right about the nitrogen safety systems, but that's for military equipment that sometimes experiences 'events' that produce a lot of sudden heat, pressure and systems' failure due to penetration by hostile weapons:
the line of seats recovered on the port side (business class?) section of twa 800 were reportedly smeared on their fabric with a red propellant produced in the exhaust of solid fuel missiles. i dunno...
my fave theory is an important friend in nyc city handing a small, cloth carry on bag to an associate and asking, 'could you give this to nicolle in paris? it's homemade jellies from her mom-mah'
back then the carry-on went under the seat...(right on top of the main fuel tank?). producing results just like in the eod momma's little helper test....
so many theories, so little time. but you're right -- nitrogen might have protected the fuel tank if the fuelage had held together at altitude until landing.
another fact we'll never know...