How to remove a table partition
Rebuild the indexes on the table to a filegroup instead of a partition schema.

Do so in the following order:


CREATE INDEX  ON [MyFileGroup] WITH DROP EXISTING on the cluster index
CREATE INDEX  ON [MyFileGroup] WITH DROP EXISTING on all non clustered indexes (one at a time)


If you can take some downtime, consider scripting and dropping the non-clustered indexes first, rebuild the cluster index and then reapply the non-clustered indexes (targeted at the filegroup, not the partition schema of course)

This is faster than merging the partitions together because it can run at high concurrency using the SQL Server index build engine.

With this trick, the schema remains in place, no need to move it all to another table. Depending on your SQL Server edition, you may even be able to do this online.