It's not rot, it's just a leaf shedding (don't remove it, let it fall off by itself) ... but I'm pretty sure it's on its way to dead. The remaining green leaves look very dehydrated and leathery, and there doesn't appear to be too many roots. It needs to be in moss or bark to maintain humidity around the roots; if it makes it, I'd suggest moss until it has several more roots, then you can move it to bark.

Thank you dannie317!! A friend of mine swears by water culture, and keeps saying it's going to get worse before it gets better. Sadly, this is much MUCH worse than what I was expecting... I might just pot it into moss if I don't see any improvement soon. For now, I'm just glad it doesn't look like stem rot...

My take on water culture for orchids is: just because you can doesn't mean you should. Orchid roots are happiest when provided with both humidity and air movement.

Yeah, plant will shed leaves and, if survived, will have long road to recovery. Better to re-train the roots for moss+small bark mixture. I resqued this kind of orchid once, it is still not blooming.