Squint query. Will it get 6/9 or worse?

If your vision 6/6 then after squint surgery you will have same vision  and you will get to See better binocular vision and steriopsis . Squint surgery is not done over cornea.. It's manipulation of muscles which hold and move the eye ball. Don't worry about Vision deterioration you can go ahead for squint surgery. (Only in very extreme squint where eccentric fixation and abnormal retinal correspondence is already developed in such cases double vision will be there temperorly or permanently in such cases squint is not adviced unless Patient, gets any benifit post surgery. And in those cases pre operative vision also in one eye usually will be very much less.) I think in your case post operative results will be better cosmetically and visually. You can send me pictures and case sheet files so I can advice in much detail of you have any more doubts.