Banks and insurance companies face different risks.
Investment banks obviously have problems with the derivatives market which may overwhelm them - as well as large corporate bad debts - however since they are actively buioding up reserves (which is why they won't lend money, put up charges etc) they should be OK.
Insurance companies have different risks - the most likely would be as a result of the cliff face at the Canary Islands shearing off - which would wipe out most of the eastern american seaboard. Since nuclear risks are usaully excluded a terrorist nuclear bomb would not cause great financial loss. The other main risk would be a natural disaster - the floods in the UK - relatively minor - still cost £100s ofmillions of damage.
Note that the 9/11 terrorist attack did not cause any problem in the insurance market regarding solvency.
One major problem is the over-supply of car insurance and uneconomic premiums being charged - this is bad for UK insurers but will not be a problem for international iones.
The biggest threats are the same ones that have recently almost ruined them ie. bad investments. They gambled with our money instead of wisely using it. Next time - if there is a next time - no government will bail them out.
Ongoing monitoring of their assets to ensure they exist and have the right value recorded in the financial records.
the global stability of world markets
Fraud by staff and/or criminals.
