Newbie w/ spondylolysis seeking non-surgical options

[dsgny]

btw: this is an amazing forum. I've just spent several hours reading and learning.

15 yo athletic son has had 10 months of Left lower back pain. MRIs & xrays showed left spondylolysis in June, and now bilateral, complete fracture but still marrow edema (grade 3). Also disc herniation L5-S1. Was slight spondylolisthesis in June, but not seen on MRI of Oct.
He's been in a lumbar corset for 6 months and stopped playing competitively 10 months ago, and suspended all athletic activity 6 months ago. He's been recommended by one orthopedist for PLIF fusion.
We'd really like to find out what non-surgical options are available and are considering (1) cortico-steroid injections to reduce inflammation around pars defect (Might the spondylolysis heal?) (2) prolotherapy (3) sonocur shockwave therapy. Does anyone know if any of these might effective specifically for spondylolysis?
Are there any other options we should be considering?
If we end up with the surgery, we're also trying to understand the differences between TLIF & PLIF as different surgeons seem to recommend one or the other, either open or Minimally Invasive. Thanks so much. :Dani