You can't destroy dltpool without destroying any copies of the data that are
in your copypool.
Essentially, if you have a backup of a file in a primay pool, and you cause
the db entry for that file to be deleted, it also deletes the record of that
file that is in the copy pool.

However, you DON"T NEED to destroy your dltpool to colocate it.
Just turn on colocation.
All output tapes from then on, in that storage pool, will be colocated.
You can let it happen gradually, via reclaim, or force the turnover quickly
by using MOVE DATA on the existing volumes.