I think you're confusing several things.
If a tag is not used on any question, it will be removed from the tag list by a daily job. You don't need to do anything.
If a tag is used on a single question and is six months old, the tag is hard-deleted from the database. No trace remains of the tag's existence, this is not a recorded edit. There is no way to prevent the deletion and even no way to monitor this short of periodically checking on the tags at risk and recording the affected questions to retag them when the tag is wiped out.
If the tag is used on two or more questions, it won't die short of someone removing it or deleting the questions.
Moderators have no special privilege when it comes to removing tags. They can synonmize and merge tags, but not delete them. So there is never a need to make a list of tags to remove for moderators. You should make a list of tags to remove in two circumstances:
- To have the tags reviewed by the community, to decide whether they are worth keeping.
- If it is determined that the tag must be removed and there are a lot of questions in that tag, developers (not moderators) can remove the tag from the database. A necessary preliminary is to have a meta thread showing consensus that the tag is to be removed.
- Additionally, on Stack Overflow only, if it is determined that a tag must die, you may enlist the community's help in intermediate cases (too many for a single person but too few to get a developer involved). This doesn't apply to other sites because retagging a lot of questions in a short time unduly bumps those questions to the front page. Again, first obtain a meta consensus that the tags are to be removed in the first place.