This is the dumbest advice i have ever heard on expired domains for two reasons,
1) you have the expired domain, the domain is expired 6 month ago, why would Google keep the site in the index, it doesn't make any sense for Google to keep empty domains listed in the index.
2) I have recently dropped about 30 domains, they all were penalized for some dumb 301 shit i did, they never recovered, so i let them go, but they are still indexed, are you telling me that you would buy them, well good luck ranking them.
Indexed or not it doesn't mean ANYTHING at all...