If the database is gone, your posts, pages, widget settings and other such data is gone. There’s no way to “recreate” the old database. You need to reinstall WP and start with a site with no content.
If you have a copy of the theme and actual code modifications, that’s good. There is a difference between what can be called the “static” content and the “dynamic” content. Dynamic is the actual page/post text content and is in the database. Static content are the theme and plugin files, uploaded images and other such files.
Ask your web host if they have a backup. And once you’re up again, install a backup plugin and keep daily database and theme backups.