In order to move your blog from Wix without SEO rankings lost, you should do that manually, just follow this transfer guide to cope with. Blog posts made in Wix come with ulr like /post/post-title. So you have to make the same URLs for the new WordPress blog. Also do not forget to transfer metatags and enable rich snippets if needed.
To switch back from Wix to WordPress you should follow these steps:
1) make sure that your previous WordPress hosting account is still active;
2) as it was mentioned above – check if the transfer was a simple dns change and if a website copy still exists;
3) if there is nothing left there, then you need to recover a website manually. If you want to see the old website structure, you may do that with a Web Archive help. Then you should make a page-by-page copy, follow the instruction to make sure you didn’t miss anything. Actually, there shouldn’t be any issues with that.
