The easiest thing to do if this where to happen, is to set up a new client from scratch.
If you have the Risk module, you will be able to print off the latest Client profile report, so you would be able to manually add the answers to the questions for the client.
If you have the Invest module, the plans that the client has will need to be entered again.
If you have the Goal module, then all the relevant data would need to be entered again. This could be done on the review date, as many of the expenses etc will have changed for the client.