Background:
My monstera deliciousa got root rot from, what I think, is inappropriate pot size. I got him in March, so almost 2 months ago, left the entire plant untouched, unwatered until all of my soil mix came in. I repotted him in a chunky, well-draining mix of pumice, cactus mix soil, orchid bark, horticultural charcoal, peat moss, and mosquito bits. Earthworm castings came a bit later and I placed a little on top. He was put back into the nursery pot it came in, but the roots weren't as well developed as I hoped, and only reached about 1/3 of the pot depth, which is my mistake.

Question:
My question is, what do I do with the left over soil? Should I sift it through for all of the rotted roots and discard them? I was hoping to sterilize it by pouring boiling water over the whole pot of soil after disposing the rotted roots. I don't want to throw away the soil either because it's expensive

Thank you so much for reading!

Its always best to throw away contaminated soil (in the landfill not your compost pile). If you can't bring yourself to do that there are ways to sterilize soil. The most common method involves baking it in an oven. Search the web for specific directions. But with all that chunky stuff in your soil I'm pessimistic it will work.
Good luck!

I sterilize mine in the oven or microwave. If microwave, I pour some water in it so it is damp before turning on the microwave. Turn on the fan either way - it can smell fairly bad.

You can pour into buckets and let it sit with betadine (povidone iodine) drench. Its a contact killer so stir it around some. I use several tablespoons per gallon but more wont hurt and it will not stain your skin or hurt plants.