https://www.legislation.gov.uk/aep/Edw1cc1929/25/9
Sections I, IX, XXIX as well as some front- and end-matter seem to remain in force.
Of course while the Magna Carta is most famously associated with England, it forms part of the law of many former colonies, for example here:
http://www.austlii.edu.au/cgi-bin/viewdoc/au/legis/vic/conso...
shows section XXIX remains law in Victoria, Australia - I imagine the case is similar in various other places.
So how does that work. If we sign a contract and I lose mine, it doesn't cease to be binding, but good luck trying to convince a court of it's contents.
Is it the same here? Could someone turn up with the 'true' Magna Carta and rewrite the law? Or does it exist as a kind of fossil in other laws?
It's very rare that contract disputes involve a serious disagreement over what the contents of a written contract were. Litigants submit their version under penalty of perjury. Mostly questions involve either verbal contracts or questions of whether additional material (specs, advertising copy) is part of the contract.
(For those who want to read the statutes "with the patches applied", as it were, Blackstones have done the work: https://global.oup.com/academic/content/series/b/blackstones... ; I remember there was something like one sentence of Magna Carta still in effect, but I can't remember which!)