Yeah you could definitely return to soil, but you might want to, lol - DWC is so much more pleasant to work with than soil and gives much better results. As soon as there's no flyers (adult winged root aphids) buzzing around the room, you can go back to soil. All it takes is one adult root aphid to infest a plant as they can reproduce asexually.
You should be able to get close to 0.5g/w if you have a good light and have otherwise treated the plants well...
For DWC, I would not put the soap in the nutrient solution, it foams like crazy with the air stone in it. Also, the point of this is to suffocate the root aphids, so there's no real reason to use the nute solution to try to exterminate, cause it's going to get aerated anyway... hence the root aphids being able to breathe. They barely need anything, just the tiniest pockets and they survive, hence the problems killing them in soil. Every time I dunked in soil, I would look at it an hour later, and see those fucks crawling around again... lots of survivors. The first time I dunked in DWC... the hydroton was floating and I saw one single root aphid swim to the surface, try to crawl on the pellet, then it rolled over and drowned... when I lifted up the bucket 30 minutes later dead root aphids just poured out, hundreds of them... and that was it. They were gone.
So yeah... just follow the procedure I gave earlier. Take cuttings, root them in rockwool in a yogurt container that's placed inside a sealed gallon ziplock (so they can't get infested) (I soak the cubes in RO water with Botanicare 1-5-4 added until the pH is 5.8 or the ppm is 200, both give the same pH). Then start growing them in the buckets, once they've rooted, which should be about 2 weeks. At that point you'll probably not have any flyers left, so long as you weren't hanging onto any soil plants (do NOT keep growing soil while switching to hydro, it just means you have to dunk over and over and it's horrible, cause they spread from the soil plant back to the hydro, it's important each of these steps is simultaneous for all plants so that doesn't happen). But if you see signs of the root aphids again, just cover them with plastic so the plant pokes out through a little slit or hole, this helps keep them out... and then dunk everything on the same day, 30 minutes in soapy water with 1/4tsp rosemary oil added per gallon of water... then rinse off the roots and plop them in fresh nutes. So long as you don't have flyers to reinfest your plants you'll get a 100% kill rate.
I wouldn't bother with the nematodes, biological controls only work to control populations, not eradicate them... I've never heard of them eliminating an infestation outright. You'll be better off religiously dunking/drenching your soil plants in 1/4tsp rosemary oil per gallon water with a squirt of dish soap... do it once a week until your plants are all finished up. It will keep the population low enough that they can grow relatively unimpeded, but if you stop they'll come back. Switch up to peppermint oil sometimes so they don't get resistance.
I tried everything except the nematodes and toxic chemical pesticides. I heard from enough people that nematodes don't eradicate them that I didn't bother, and around the time I would've tried them I thought of the DWC dunking idea. So I tried rosemary oil, peppermint oil, cinnamon oil, neem oil (they loved this, the population exploded after that LOL), tobacco tea (didn't even flinch), diatomaceous earth, dunking, drenching, covering the stems and the sides of the pots with tanglefoot to trap ones that crawled out during the drench which killed thousands, it was disgusting dead bugs on top of dead bugs in that horrible goo of doom... it was the tanglefoot/trapping them in the goo idea that led me to the DWC one... basically I realized the problem wasn't that we didn't have ways of killing them, but that they could escape the killing agent (breathing air bubbles or crawling out), the DWC dunk makes all that impossible, no air pockets to be found there and no way to crawl onto a hydroton pellet, it just rolls over when they climb on it and dumps htem back underwater. The ones with wings would fly out of the soil and get into the foliage, waiting for the soil to dry enough for them to return, so that's why the tanglefoot idea ultimately failed... that's why I covered the plants in hydroton with plastic around the stem, so those guys would be SOL.
Try dropping your plants into plastic grocery bags, and tie them closed around the base of the plant... it'll keep the flyers from coming out and getting stuck on the buds.