A truncate that deletes indexes?
I find that hard to believe, for that index to dissapear, you must have some other process removing it.
From sybase documentaion on IQ 15.4
TRUNCATE TABLE is equivalent to a DELETE statement without a WHERE clause, except that each individual row deletion is not entered into the transaction log. After a TRUNCATE TABLE statement, the table structure and all of the indexes continue to exist until you issue a DROP TABLE statement. The column definitions and constraints remain intact, and permissions remain in effect.
1- You create an index and its in effect. Just keep it up to date.
2- Well yes the index has no rows to "index" anymore, but it still exists.