While not 100% similar, I recently flew SIN>NRT in D1 on a cleared GUC, then attempted to fly NRT>DTW (also on a cleared GUC), but, without getting into the nitty gritty of the issues on the ground, ended up missing the flight (along with everyone else on the SIN>NRT flight) through no fault of our own, and ended up spending the night in NRT (terrible). Anyhow, the point is, I wrote to DL about our experience and they ended up re-instating the entire GUC for my wife and I for the trouble, even though SIN>NRT cleared (and we flew it). As with most things, it doesn't hurt to ask, they have the power to give you the GUC back, and given this was a crew/seat issue on your part, they may take pity on you. I think you have a relatively good case, given you stated you might not have used it just for NRT>SIN