In the past, I cleaned quite a few infested lenses. Nothing that expensive though; mostly no-name 135/3.5's and such, one 50/2; basically, stuff that was more expensive to return than to trash. On all lenses I cleaned, the fungus went off easily with isopropyl alcohol and ammonia-based lens cleaning solution. No visible traces of it were left on the coatings (I looked hard). 3 years later, no growth re-appeared in any single one of them.
That said, I would rather return the 24/2.8 in order to get a healthy one. Lens too expensive and risk too high.
Only one lens that I've seen was damaged by fungus beyond repair; that was a Tamron SP 500/8 mirror, and that lens went back to the seller the minute I took it out of the shipping box. Apparently, it was "cleaned" by the seller, but I could easily see the damage in reflections.