If you have proper maintenance records and know for sure that oil was changed frequently (and hot!), I wouldn't worry too much.
A particular MB mechanic comes to mind when he told me that he never ran across a late model (1990-91) 560SEL that had a broken chain.
I'd do it for peace of mind before 200K miles... Mine has 103K and will see this work done sometime in the next year. Again, peace of mind, so I'm good for another 100K!