Very nice. I like how you wove this into canon, yet rewrote it as well. The mood and pacing and introspection is great. I agree with the other reviewer who said they liked mature!Harry; how he actually thought about the decision beforehand (despite his propensity to dive right in, as you say) and ask Severus before proceeding, to really give him that choice. It's something they've both had very little of in their lives.
I don't think the ending is a cliffhanger, though – not really. I simply anticipated you would end on a piece of dialogue or something to nudge a little more outcome. It felt a tiny bit unfinished. I can make a good guess that things work out... but maybe not, too. I was fully expecting you to do the super-angst route and have Harry go through all that work and then Severus wakes up with no memory of the conversation he'd just had in his spectral form. It'd be back to his snarky self who berates Harry for bringing him back, then proceeds to hide his true feelings by outwardly putting Harry through mountains of angst before eventually succumbing.
Because that's your thing! *grins*
But, yes, even so, I'm glad that it seems they will get a chance to do this properly and both be happy. I think that is the ending you meant. *eyes you*