Yes, this happened to me. I had befriended an IP, turning it into a city-state. Before I could get my missionary down there, an AI rival had sent its military to the CS -- conquered it -- and started the multi-turn raze. In Civ3/Civ4/Civ6, razing is instantaneous. In Civ5/BERT and now Civ7, the raze takes multiple turns.I'm finding I can't convert city-states to my religion on my current save; this is the first time I've ever tried as far as I can remember. Whenever I move my missionary to a city-state, the "spread religion" button is greyed out and the mouseover says "Spread Religion cannot be used on a settlement that is being razed". This must be a bug, right?
In previous games, though, if an AI captured one of my cities and started the raze, it was possible for me to recapture it and stop the raze. I hope that still happens in Civ7 (I haven't lost a settlement yet). I would be even happier if it were possible for me to recapture the city-state, "liberate it", and stop the raze.