Eq "rotting" is not an instant "wups, it went from great cond to zillions"
situation. It is relatively constant and, more importantly, slow. If you give
your eq to a merchant and it rots to pieces faster than he can repair it, this
is YOUR fault for waiting so long to get it fixed. A goblin with a magic
missile could have done the same thing.
Along the same lines, unless the merchant is either ripping you off or
incompetent, they should not have your eq so long that it rots by any
significant degree, and even then, you can make them repair that too.
The issue of "eq held by merchants should not rot" is a non-issue. You are
panicking over nothing. Get back to killing bunnies.