The API is down because our new generously-provided hosting does not support executing arbitrary code on the server. Without this provider the site would have been taken down again already, so we are grateful for what we've got.
Once they've submitted a DMCA notice, the hosting company has to take it down within 2 days unless you file a counter-notice, which has to personally identify you and be signed "on penalty of perjury".
None of the DMCA process has anything to do with whether the claimant has a legitimate copyright claim over the work.
Their legal team is vicious about taking down any open-source implementation of the W3W encoding algorithm. This is sad because it could be legitimately useful in a small handful of circumstances, but only if it were free and open to all.
We released WhatFreeWords last week and it was taken down after 4 days.
Patent documents can be very useful, particularly in areas where the patent is unenforceable.
My team found the what3words patent very useful in reverse engineering the what3words geocoding system, and have open-sourced our results: https://whatfreewords.org/