Forever at his Fingertips
In a way, he thinks it was best that he was the first of the Lestranges to die.
Not in the way that his death was a sacrifice so Bella or Ro didn't have to die then, he knows he's not that selfless, Merlin help him if he was, because he'd be dead a thousand times over.
No, it's because he doesn't think he would have had the strength to watch either of them die. It's not that he has no friends, or he doesn't care about them, but purebloods are brought up placing the utmost value on family (not only for the sake of blood purity, but to love and to cherish, because purebloods are a dying breed, everyone knows, so value what you've got while you still have it, that's basically what it means, he thinks).
Rodolphus taught him that. Their father was dead before Rabastan turned two, and their mother shortly after his ninth birthday. He loves Rodolphus as a brother, and Bella as though she were a blood relative, and he thinks, no, he knows it would have driven him mad to see either of them fall.
His grip on sanity isn't that strong, he knows, but when the bloodline looks near extinct, does it really matter if one's descendants have homochromatic eyes or whether they're entirely stable? Family first, no matter what.
Besides, the eyes aren't that bad. Rabastan thinks they give him an aura of edginess, something a little mysterious and different. Rodolphus laughs whenever he says that, and tells him they just make him look like the result of a potions experiment gone wrong (all the while pointing out his own two matching green eyes, then ruffling Rabastan's hair to make sure he knows he's just teasing).
He's done that forever, since Rabastan first realised it wasn't quite normal to have two different coloured eyes, up until the day Rabastan snuffed it.
Rabastan won't ever admit it, but he likes it when Rodolphus does that. (Did that, he corrects himself, he's dead now, and Rodolphus isn't, so they're going to have a hard time teasing each other.) It's been his constant (the thing he could always rely on to tell him whether or not he and everything around him were real) through all the years, and it was that which convinced him that everything was okay (even if it wasn't forever, even if it wasn't perfect, it was okay) after Azkaban.
And it was. Everything was okay. Maybe they weren't quite the same people as they had been before (they all looked older, certainly, and it wasn't just the subtly aged facial structure, but something else, something they all knew, something deeper than skin, muscles, and bones, possibly deeper than their very souls, or at least on the same level as their souls), but they could reform their lives, they had a home again, a master to serve, a cause to fight for. It was like being born again (only not, as babies never know what they have to do until much later, and they knew it straight away, and they were ready for it).
That was what Rabastan had thought while he lived, but now he knew it was really more like dying, dying and waking as almost the same person (the only difference being a profound change that couldn't really be described, something beyond words). He is different now, (he can tell, and so can his parents and his friends who left their mortal lives before him), changed in some way of which he isn't quite certain. Everyone else is a bit different too, in the same way as he is, so he knows he's not going (more) insane.
Evan advised him not to think about it too much when he woke after his death. It would drive him to obsession, Evan said, and obsession is another step on the road to insanity.
Rabastan doesn't want to go insane, not yet, he's waiting for Ro, and Bella, and Antonin, and Lucius, and Augustus, and Walden, and everyone else, and he can wait forever because he knows (now) that no one lives forever, while in death, he has forever at his fingertips.