worth the repair?

Are you using the the pre-out or the tape out RCA jacks of the Marantz?

There's multi meters out there dirt cheap you can test the resistance of the speakers. Each speaker should have the same number. My speakers were 4.3 so once you determine if speaker is or not fried stop using the receiver and integrated together (for now) and use 1 and then the other. If everything survived your experiment you got lucky, but likely something's toast and now you know which it is.

 Can you switch the speaker leads to make sure it’s not the speaker that’s gone out?

@pharmacylaw - specifically, how did you connect your Marantz Receiver (used as a passive tuner) to your McIntosh (amp)?  If connected incorrectly, component damage may result.

An amplifier expects a small signal to amplify, so it’s very bad to connect it to another amplifier.  Both Marantz and Mac have amplifiers, but the Marantz has a bypass connection (preamp out) that bypasses/skips the built in amplifier.  Also, it’s best/safer to minimize both volumes before powering up

Yeah this is a weird setup.  OP you need to explain exactly what you did as you connected two pieces that essentially have the same function.  

Also, typically if an entire speaker goes silent, it could be a fuse issue. 

But first, how the heck did you have this gear interconnected?