Oncidium 'Dancing Lady' with selective root rot...

[OrchKid]

Hi, folks - this is my first post (have been lurking since I set up an account, sorting through what I can find here). Am hoping one or two of the many fine knowledgeable people here can help with my plant issue.

And I did search the site, but didn't see much about damage just on the top of the plant.

So: I brought home a dancing lady oncidium from a nearby research gardens in mid-Judy, well in bloom. It unfortunately came with its own set of aphids; so I clipped the spikes and successfully dealt with the bugs. Pretty soon afterwards, it sent out a growth and is now 5" into a new pseudobulb (yay!).

I checked the roots at that point and they looked white and healthy, though crowded a bit. It's in a 3" square plastic pot with just sphagnum moss (from what I can tell). Given the new growth, I decided to wait until it started sending out roots before repotting.

So we settled down to a once-weekly soak for 20 mins, with weak MSU fertilizer once a month. It sits on my dining room table near a west-facing window (and a view of the house next door, though there is afternoon sun). And it looked fine. (Even with the cat occasionally chewing a leaf tip or two. )

Except in the last week or two, the aerial roots have started looking brown and moldly. BUT - the roots in the pot still look fine. So I'm not sure of what to do about it.

Some thoughts:
1 - Cut the aerial roots off, spray with copper fungicide, return to original pot.
2 - Cut off the aerial roots, spray with copper fungicide, put into a round 4" ceramic orchid pot.
After reading a few things here:
3 - Pull off the rotting part of the roots but do not cut, spray with copper fungicide, leave in pot.
4 - Pull off the rotting part of the roots but do not cut, spray with copper fungicide, transplant.
5 - something else I didn't think of.

Help! Because this was a semi-birthday gift, it was doing okay before this, and I do think I can save it.

Will the loss of the aerial roots heavily impact the health of the plant?