I was scanning the tag list for Mathematics, there are loads that have never been used and probably never will be. Can anyone nominate a tag for burnination, is there procedure to follow, and who decides a tag's fate?
From the sound of it, you're talking about tag synonyms, which will never have any questions by-design! They exist to guide taggers to use canonical tags, and the system automatically replaces them with the tag they're synonymized with whenever they're used.
Beyond that, unused tags are deleted every day. Tags used on only a single question are removed 6 months after their creation, unless someone has taken the time to write a tag wiki.
For all other tags, they can be removed by following the instructions here: When to burninate
A tag should be removed when it's being harmful: when allowing the tag to be applied to questions results in weaker classification of questions. A recently killed example of such a tag is intersection. An example that's still alive is transformation. These are problematic, because people use them instead of picking another tag that would unambiguously describe the subject of their question.
On the other hand, low-use tags are rarely a problem.
- If a tag indeed is not in use, it will be automatically deleted with no action on your part.
- If "probably never will be" used is a pure guess on your part, that's not a reason to remove the tag.
I was going to link to Shog9's answer on Meta.SE, but now that he already did that, I'll just quote two points for emphasis.
don't bother with this [retagging to kill a tag] unless you have full editing rights.
If it looks like pointless busywork, it probably is pointless busywork.