I've given this some thought and it's quite reassuring. But I'm left wondering, if Medium essentially indemnifies writers, why didn't they tell me this when I asked?
I wrote to them asking if there were any measures in place to protect us from legal demands like this - and I sent them a link to the Unsplash case. They didn't answer the question! So I took that as a 'no'.
Also, these demands for payment usually cover the period *before* the take down notice. So I'm not sure deletion solves everything. But it would be nice if it did. 🙂