Well its said that everything happens by fate , nothing in our hands , even postponing delivery time too done as per fate . birth chart is blueprint of your past deeds , whatever we have done we should undergo that . if person is destined to get cured , he indeed recovers , even for rare dangerous disease persons gets medicine somewhere suddenly , its all destined in chart .
Day which you selected for surgery is very good , it also sync with your husband horoscope . that day falls in Revathy nakshatra which is ruled by mercury . as per rasi 6th lord venus is 10th also venus mercury are super friends so you can continue . also he has Tara bala - method to calculate particular day is auspicious or not . it also nice . everything aligned in a way that fate is favorable for your husband .
he is cancer lagna and saggitarus rasi . 1st lord in 6th aspected by saturn who is 8th lord , mars too aspects 6th house , its good . but saturn heals slowly . also he currently undergoing moon dasa who is his 1st lord in 6th . thats y the problem . saturn is a slow healer mars is quick healer , his mars dasa gona start soon and will completely recover fully . next year will be very good for him. but for now this moon dasa will give temporary trouble. both moon(1st) and saturn(8th) has equal power , that why your husband withstanding all these illness ,. indeed with his will power he recover soon .
After 2021 march he gets very well . all his problems cured .
General note - Any medical treatment which is taken on days which falling Aswini nalshatras and or Tuesdays gives excellent results .. ( this is not applicable for emergencies ) ..