Koga touring bicycle bottom bracket loose, does it need replacing?
Hard to say without knowing a bit more.

The BB could use a cartridge or could use loose bearings.  With loose bearings the situation you describe would generally only happen if one of the cups came loose, in which case the balls could slip out of their races, leaving you grinding metal-to-metal.

With a cartridge, if the cups retaining the cartridge get loose the cartridge can slip-slide around a bit, but a real problem would only occur if a cup came loose enough to let the end of the cartridge slip out, at which point the cup would be nearly ready to fall out anyway.

Either of these loose cup scenarios would be immediately obvious to the trained eye of the service tech, without having to take the BB apart, and either could be simply rectified.  So more likely there is a cartridge and it has come apart internally (though along the lines of the loose bearing scenario).

Normally a bottom bracket should last a long time.  Loose bearings can be repacked every 10-20 thousand km or so, and cartridges may need replacing at maybe 50,000 km.  The type of failure you describe (absent the involvement of a clumsy mechanic) is unusual.

If indeed the cartridge has disassembled itself internally then probably no great harm would come from riding on it, other than it could lock up suddenly without warning, or at the very least leave you stranded somewhere.  But with a loose cup scenario you should not ride the bike, as this could damage otherwise-repairable parts.