Starting in early April, Bethesda.net Launcher users will be able to migrate their library and Wallet to their Steam account. Many games will also have their saves migrated, with a few requiring manual transfers. For the games that require it, you will still use your Bethesda.net login to sign-in and play. In the future, Bethesda.net accounts will remain accessible on Bethesda.net, and future titles will continue to support those accounts.
For more information, visit the full FAQ on Bethesda.net.