There is no water or oil cooling on the gearbox.
1, The gearbox itself may have failed internally, this is not uncommon . Needs removal and dismantle to identify the issue.
2, the clutch or clutch operating slave cylinder may have failed, gearbox removal required to access.
3, the part of the drive shafts connecting the hubs to the gearbox may have failed.
4, the linkage/ cables from gear selector to box may have broken.
1 , very expensive, 2 slightly less expensive, 3, moderate cost, 4, moderate cost.
Get recovered to a garage so they can confirm whats happened. If gearbox failure has occurred, then recovery to the UK is your best option.