My CRS said my fissure is very deep too with exposed muscle, but he wasn't a fan of cleaning it up and neither was I. A different surgeon I saw wanted to clean it up and use botox but I went with the LIS only instead. The CRS I went wit said a fissurectomy (if that's what you're having) can take a bit longer to heal, but if its what's needed then its probably a good idea.
I'm in the process of healing from an LIS I had two weeks ago and it wasnt as bad I thought it would be. The surgery pain was less than the fissure pain.
I find soft boiled veges like brocolli, carrots, peas etc are good and that chicken is better than red meats. After surgery keep a jug of water by you as well as some pain meds, which you may not even need. I only took strong ones the morning after surgery and then went to paractemol. The fissure pain was less and the surgery pain responded much better to the paracetamol than the fissure did.