Generally if the retina is going to detach there are symptoms such as increase of floaters, bright flashes of light and possibly loss of peripheral vision. If you had those you should have reported to the cataract surgeons office. But that is water under the bridge. You have a very serious problem these are my suggestions:
1. Your most important eye is the one that has not had the retinal detachment (RD). The chance of a RD in your "good eye' are very high, as has as 3-10% depending on what the retina looks like in the good eye, degree of myopia, presence of lattice degeneration. I would be sure you see a retina surgeon every year (in addition to a cataract or general ophthalmologist) and it is a full out emergency if your good eye has sudden onset new floaters, flashes of light or loss of peripheral vision.
2. Even if the retina surgeon takes the oil out of the back of the eye the chances of that eye having good vision are very small. You should ask both your cataract surgeon and the retina surgeon "Did I have a macula off retina detachment" if the macula was off normal/good vision unlikely. Also ask "What does the macular OCT in my RD eye look like? Is it normal or abnormal, how abnormal:
3. I would strongly suggest you see a DIFFERENT retina surgeon for a second opinion about the oil, and about the prognosis for vision if the oil is removed. ALSO a careful exam of the good eye and ask about retinal abnormalities and the chance of RD in it.
4. I cannot tell from your post if the good eye has had cataract surgery. If it has NOT had cataract surgery the risk of RD will increase significantly if it has to have surgery. If you have cataract surgery on good eye, you need exam by retina surgeon and clearance for surgery and need to be seen in the post operative period by retina surgeon.