Not A Smart Move

Don't worry. If she wants to divorce, there are lots of tunnel is waiting for her in Paris. Accident can be happen always! RIP Diana!
 
If the law is similar to here, it's accumulated wealth since the marriage excluding child support. She has $ 5 million of her own and probably lucrative potential tell-all book deals that could more than double it.
 
Unless for some bizarre reason she is having to spend her own money for routine living expenses, with millions of dollars in assets, should the whole thing fall apart (which one would hope none of us wish to happen in a marriage), I doubt that a judge would grant alimony. Hence the lack of a prenuptial agreement is not as great a risk as it might be in other situations.