I think the first thing to say is that nearly all floods are avoidable. Most are caused by user error of one kind or another. Probably the most common cause is lack of attention to o-ring cleanliness (trapping dirt or hair or whatever). If you are paranoid and disciplined you will be OK. But that wasn't your question...
Of course it depends what degree of flood happens. Again I think partial flooding is more common that total, i.e. the housing has water in it but it may not be full.
1. The camera is most vulnerable. The battery is almost certainly shot. The body itself is probably done if it was really submerged. However, there are shops that specialize in recovery after water damage and they claim good success. Most of the time the memory card will be OK. So if you have pics they should be retrievable.
1b. The lens probably has a better chance unless it was fully submerged. Today's lenses have plenty of electronics in them, however if the housing was partially flooded the lens may escape the worst of it.
2. Strobes usually flood the battery compartment. This is usually a relatively cheap repair ( I have done it with ike strobes). The batteries will be shot and should be removed asap to avoid further corrosive damage. Damage could cost about $100 to fix which is not too bad compared to new strobes.
3. You can make this calc yourself by comparing the policy deductible + premium and the cost of the damage. Depends on the specific policy. H20 insurance deductible for flood damage is the greater of 10% of the claim or $250. Premium depends on value insured, you can easily get a quote. Don't forget it is for a one year policy, so it depends on how many dives you are doing. If you are doing one trip, five dives: that's one value assessment; if you are going to dive all year 100's of dives, that's a different value you are getting for the same premium. Also the insurance covers other things such as theft with a lower deductible. So that has a value too.
Hope that helps, others please jump in.
