That's bad luck. That hole is pretty much where the diff pin usually ends up smashing through the casing...and it can be repaired. I had an Alfa refurbished 6 speed GTA gearbox with a repair patch right around there.

The hard part will be stripping & cleaning it for welding. Fortunately, these 6 speed gearboxes come apart pretty easily. De-greasing it for weld will be the hard part.

I've never seen a rivet on a clutch fail like that.