-
Depends on the axles and how much you, sorry, your friend, cares about the bike. You’d want to disassemble the hubs in any case, to let them dry out and get any stuck water unstuck.
Easiest would be loose bearings - just take apart, clean, regresar and reassemble. Would do the same to the freehub and RD jockey wheels if you can.
Sealed bearings you can still clean and regrease but they take a bit more effort, especially if they’re pressed into the hub: pry off the seal, clean with degreaser and a brush until liquid runs clearish, regrease and reseal. Alternatively, wait until they break and replace. Still worth airing out the hub IMO.
Obviously one should never ride through flood water as it is hazardous in many ways but hypothetically if you did and it was deeper than one anticipated and over ones axles what sort of bike remediation should be carried out afterwards? Asking for a friend.