Megacolon Surgery (does it work)

If a cat has megacolon surgery, would it fix the constipation issues and make the poop soft? 
Should I wait until I find a way to make my cat's poop soft before proceeding to megacolon surgery? 

I tried everything, miralax, slippery elm, lactulose, pumpkin, cisapride, agar agar, guar gum, they all worked at first, but my cat got adapted to everything and they no longer work   

p.s.  he's in an all wet food canned grain-free diet

From what I have seen here the results on this surgery are mixed.  It is a big surgery with a recovery period.  I would talk to your vet about it, whether or not to try the surgery is a very individual decision with a lot of variables.