The region of memory associated with a MEMPTR variable remains allocated until it is freed. ABL does not automatically free the memory for you. It is up to you to ensure that the memory is freed.
You can free the memory using SET-SIZE with an expression of zero (0). SET-SIZE then deallocates (frees) any memory region associated with mptr-name. This makes mptr-name uninitialized.
Note: You must fully understand the memory management provided by shared library routines before you can effectively using MEMPTR variables with them.