This was a bit of a discussion item some time ago with a TRE I was chatting to. I asked if the thrust lever would actually retard to idle, as on another type I fly it snatches back violently if a reverser unlocks.
The FCOM is silent about it, but if you dig into the QRH, the first step gives you this:
1 Check movement of the forward thrust lever on the
affected engine.
The EECs prevent power above idle if the related
thrust reverser has moved from the stowed
position.
The TRE I was chatting to tried it in the sim and nothing happens. When you think about the AT behaviour this makes sense - with the AT disengaged, the T/L servos are disengaged so cannot attempt to move the thrust lever. With the AT engaged, the servos are commanding a T/L position to meet the demanded speed. I suspect for fear of unpleasant failure modes Boeing decided not to have the thrust levers retard automatically for failures.
It does make sense to have the EEC limit thrust, as Reverser status goes directly into the EEC anyway.