Long running index rebuild I'm running an index rebuild using Ola Hallengren's script below.

EXECUTE dbo.IndexOptimize
 @Databases = 'insight',
 @FragmentationLow = NULL,
 @FragmentationMedium = 'INDEX_REORGANIZE,INDEX_REBUILD_ONLINE,INDEX_REBUILD_OFFLINE',
 @FragmentationHigh = 'INDEX_REBUILD_ONLINE,INDEX_REBUILD_OFFLINE',
 @FragmentationLevel1 = 5,
 @FragmentationLevel2 = 30,
 @LogToTable = 'Y'


It has been running for almost 2 days. How bad would it be to kill the job? The index it is running against is 78% fragmented. The table at issue has 111,543,114 rows.
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.