I noticed more and more people are complaining that their wikis got closed for some reason here, so I'm just going to give the most common reasons your wiki might get closed.
1. It's Inappropriate []
If your wiki is only just spam or contains extremely obscene, hateful and sexual topics with pictures, don't expect it to last long. You will also get globally blocked for it too.
2. It's Inactive and Contains Very Few Pages and Edits[]
If you and your community are inactive on your wiki, and made very few edits and pages there, expect the wiki to be closed. However, if a wiki has an inactive community, but has a lot of edits and pages, it'll most likely not be closed by FANDOM staff. I think that wikis with at least 50 or more pages with an inactive community are more likely to not be closed than wikis with less than 50 pages that have an inactive community.
3. It's Literally Copying Content From Another Wiki[]
If you make a wiki that has the same content and style as another wiki, expect it to be closed and possibly merged.
4. It's a Harassment Wiki[]
If you made a wiki just to harass and insult users here, expect the wiki to be closed and you being globally blocked.
If your wiki is not any of these 4, then your wiki should be safe. However, sometimes wikis get closed for less obvious reasons than these 4, so basically be careful on what you and your community make on that wiki.