Emergency orchid rescue - only air roots

[Kristyn'sOrchid]

Hello everyone!
I desperately require guidance about how to revive an orchid that only appears to have air roots left. The plant was given to my husband by his now deceased mother. After many years of caring for the plant, it has taken a sudden turn for the worst. It appears that the roots must have been over-watered recently and now only two roots are left - although they are not in a good condition (only one seems to not have rotted away). However, there are numerous air roots on the plants. The plant has only just finished flowering. Should I cut off all the old roots and stem and simply pot the aerial roots? I have the aerial roots soaking in water at the moment as they were quite withered and silver-grey in colour.
Any advice would be greatly appreciated.
Thank-you all so much!