Long running index rebuild
You should be able to see if it's doing a reorg or a rebuild by using sp_whoisactive or something similar and inspecting the sql_text column.

If you kill it, you will not lose the work it has done on previous indexes that were defragmented as part of this script.  Those are done and committed.

As for the current index it's defragmenting, if it's doing a reorg, the progress it has made will not be lost if you kill it.  If it's a rebuild, which seems to be the case given the data you've provided, it's still OK to kill it, but you will lose any progress that has been made.