I asked the Headmaster to go back and save Hermione and then fake everything, fake the dead body, edit everyone's memories, but Dumbledore said that he tried something like that once and it didn't work and he lost another friend instead.

This sentence is interesting - not least because I had previously assigned a high probability to this being his method of resurrection, but also because it potentially tells us interesting things about time and death in the MoR-verse.

... I'm not entirely sure what, though. That last bit, in particular, that someone else died too when he tried...