Still thinking the "finality" doesn't work:
They don't even *have* to be buried in NYC - they just *have* to have the gravestone with that inscription placed there. That's *it* - that's all that their "utterly final" fate actually requires. They canl be back if the actors feel like it.
It's what I said about needless arc and hype - if they'd just done the episode and moved on we'd all be thinking "cool, they live out their lives in the past" but by going on about the finality of how they can never see the Doctor again, it just makes us go "but they can if..." Moffat's a great scripter, but their grasp of publicity and guiding the audience is totally borked.