Another question: Your exchange goes offline after I send you my bitcoin but before I receive my ether. How do I continue with the swap process with the website being offline to get my ether?
Excuse me, did this actually happen to you, or is it just a hypothesis?
If this actually happened, it's a serious matter, and the service must prevent such incidents from occurring, as this would quickly damage the site's reputation. If this is an example, I believe OP should clarify, since he claims the service is decentralized and the user has the access to obtain the secret key to the deposit address.
Unfortunately, OP continues to insist on not disclosing the domain name they've been using since 2018 and has refused to even provide a valid reason for doing so. At the very least, he should have refrained from claiming the service has been active since 2018 if he wanted to keep some details private.