They probably won’t break compatibility with Vaultwarden on purpose since that’d also break their own server implementation. Bitwarden would have to ensure that all selfhosted servers are up to date before pushing a breaking auto update. This likely means enough time for vaultwarden to catch up.
Few things hurt a company providing critical software more than breaking users access without notice.
The passwords would still be accessible through the webui anyway.
Edit: If your not comfortable it’s better to not use it. Password manager are critical and have to be trusted.