Being quite honest, oxygen is just fine for roots! The problem is that the roots were exposed to air (which is not just oxygen, but a combination of gases), completely drying them out.

There is hope!

You should cut off any unhealthy (yellow or brown) growth.

That pot is also a bit too big for the plant (it will be even bigger, once all dead/unhealthy growth is removed). Hoyas like to be a bit potbound.

You should make sure that the mix you are using is fast draining (and also make sure any pot you use has adequate drainage). Depending on your location and climate, a fine grade orchid bark mix with a handful of potting soil (I personally don't use any soil; it holds too much water for my climate, and compacts, disallowing drainage through the pots) mixed in.

Do not over-water; that is the #1 killer of hoyas. Water only when the top inch/inch and a half of mix is dry. Feed each time you water (water soluble fertilizer at 1/4 strength- I use MiracleGrow water soluble Tomato food; it's cheap and provides the essential nutrients).

Taking backup cuttings and rooting them should also be done, in case the mother plant declines and cannot recover.