Depends on what "degradation" means.  If it means the margins aren't
perfectly smooth, no.  If degradation means a significant fracture or
evidence of decay (explorer stick) then yes.
    IOW, the word "degradation" as such is meaningless, and you deserve a
real explanation for why the dentist thinks the filling should be replaced.
    There are a variety of reasons why there may be problems after
replacement--these should be figured out so that the chances of it
happening again are minimized.  This doesn't mean you don't treat decay
 (obviously), but unless the cavities are very deep (in which case
postop sensitivity can be predicted), it shouldn't happen.  If postop
sensitivity happens routinely something is wrong.

Steve