Is it possible to migrate a wiki.fandom.com database of almost 1,000 pages to a mediawikia.org project without having to redo each page.
Topic on Project:Support desk
Basically, yes.
For a good programmer it is no big deal to populate a wiki automatically from any external source.
There are some WMF wikis which are almost only written by automatic bot activities.
I don't know what mediawikia is. Do you mean mediawiki (us)? We don't host projects, just provide the software. You can use the software to host it yourself. Otherwise try contacting miraheze or shoutwiki if you're looking for a fandom like host that is not fandom.
Maybe wikia.org?