the cutler's cement used in nepal is 'laha' made from tree resin, bit of bees wax, and fibrous filler additives, plus some brick dust etc. the brick dust may give it a reddish colour.
the most common fibrous material used is dung, which contains a lot of undigested plant fibre and some seeds. gives it a lovely aroma when heated to melt it. i would suspect the indians used much the same resources
a more modern thermoplastic, solvent based cement, gorilla glue, or two part epoxy would be inappropriate
the story is told that some untrusting commanders of native troops would keep the blades and grips separate in their armouries, and only marry the two (with the cutler's (thermal) cement/mastic) just prior to going to war. helps cut down on mutinies if it takes longer and more obvious signs of the lower ranks starting to arm themselves. not suire how true this might be. anyway, more freshly melted cement may indicate more recent reconnection of the blade & grip, which may be much older. they did not generally pin or peen the tangs on the tulwars together permanently.
p.s. - looks like a nice heavy sword. worth polishing/etching a small spot to see if it is wootz. the markings look like someone tried to islamisize (sic) the decor which may indicate mughal connection rather than a hindu/buddhist area as the source.