They will need completely stripping down pretty much as far as they will go. Electrics/electronics are likely to be irredeemably fecked, engines/transmissions need to be fully stripped, the list is virtually endless. Im not sure of my facts here but seem to recollect that if the water was contaminated with sewage then they may not even have the option of salvaging them, insurers (if they are insured) may be under a requirement to ensure they are destroyed. It could be different in France of course, but speaking from some anecdotal chat from a relative who was flooded out in the bad weather a couple of years ago - he wasn't allowed to have some of his possessions' repaired as they were contaminated, they were whipped away and destroyed.