I would hate to lose Kai and then to only have this problem come back to a nother fish down the road..
No, you'll be fine. The clowns won't pass it on and the best way to make sure you've cleared it out from the tank is to persevere with the same fish that had it in the first place. That's how I knew it worked for me. I had my clowns when I still dealt with hex...All has been fine for years since and many fish share the same space, including new clown loaches, and none have shown signs of hex re-curing since...
I think I mentioned it to you already, and it had completely slipped my mind earlier in this thread, but I'd suggest replacing further levamisole treatments on any fish with flubendazole, because flubendazole, metronidazole, dimetridazole, mebendazole, etc.....basically anything that ends on "zole" treats that nasty bug with many names called hexamita/spiro/HITH, etc.., just different dosages/treatment methods and all have different toxicity/side effects.
Flubendazole is by far the safest of all of them from my research, won't harm young fry.....

The advantage of flubendazole also is that it also treats round worms and tapeworms apart from parasites such as spironucleus vortens....so it would have covered the capilaria worm issue too...You may need repetitive treatment for hex, but so does a metro treatment. Flubendazole won't harm fish's liver unlike excessive metro use and has quite high overdose tolerance..
I mean, generally speaking, there are so many options to treat hex...At least we do here in Europe, tons of different meds for it......Question is, does your fish still have hex? With a microscope on hand I won't approach any treatment until I confirm the fish is infected. " A hole in the head" can be caused not just by spironucleus vortens.....It could also be a dead worm tissue, e.g. remaining dead capilaria worm and what you see is the fish's immune system response trying to expel it...Similar to if you have a thorn in your finger.....
Which reminds me...levamisole, although effective against worms, can be in cases lethal if the fish is over-loaded with worms, because it kills the worms inside the fish, and if the fish is not able to expel the worms, they can die.....At least that's what I remember from the top of my head about it..., meaning it killed the capilaria worms, but it is up to the fish to expel them from their body....(levamisole is not effective against hex).Flubendazole on another hand starves the parasites/worms. Metrodinazole stops the parasite/hex from re-producing...So different meds treat in different ways....