What maintenance should be performed on the table after a massive
When performing a large delete like this, SQL Server doesn't actually remove the data from the pages for you right away. It marks them as logically deleted and the ghost cleanup task will then remove them as it runs in the background. That said, here are two questions you can ask yourself:
Does the table have a clustered index?
If so, rebuilding it will remove the deleted rows. If not, and you don't want one, consider building one and then removing it. Otherwise, a heap table can suffer from various issues like forwarded rows, etc.
Is this a large table?
You've mentioned it is, so the statistics that are automatically updated by SQL Server will not be sufficient. You will want to perform periodic UPDATE STATISTICS to have SQL Server sample the data (or force full scan) and update the statistics accordingly. As an alternative, consider rebuilding the table indexes as a way of also triggering an update to the associated statistics.
Review whether you have/want a clustered index on your table and make any necessary changes. Then, rebuild your clustered index (or non-clustered if a conscious decision has been made to keep it a heap table). When rebuilding the clustered index it will cause a rebuild of the non-clustered indexes as well. This is because non-clustered indexes point back into the clustered index if one exists on the table.