Assuming this is an Indian blade that was originally fixed to a 'tulwar hilt' ...I would suggest that the rivetted crossguard was functional. The tang on such a blade would have been relatively short....compared to that of a kaskara blade.
To 're-inforce' the tang fixture, rivetting the crossguard through the blade makes sense ....bearing in mind that part of the 'langet' is bound/fixed to the hilt. The langet above the hilt is in fact wider, it is one piece with the lower section but 'stepped'.....this again suggests that a 'good, solid' fixing of the crossguard to the handle was required ....to which finally the blade was rivetted...
I am assuming that ... indeed, the rivet passes through the blade ....so is just pure speculation
Regards David