Horry's clutchness was only about 1% of his value to the Spurs. Horry's defense, screen setting, passing, knowledge of where to be and his overall basketball IQ were only traits that were much, much more valuable. If Diaw plays like Horry but misses every clutch shot, he'd still be a huge asset.
Pop's Big 4 is a lock to be in the rotation (Duncan, Ginobili, Parker and Bonner). Then we know Jackson and Splitter will get some time. Eventually you gotta think Diaw takes Blair's minutes. Behind Parker, it'll either be Neal or Mills. Then there's room for another swingman, which will be Leonard, Green or Neal (if Neal isn't the backup PG).
My guess is the rotation will eventually look like:
C Duncan
PF Diaw
SF Leonard
SG/SF Jackson
PG Parker
C Splitter
PF Bonner
SG Ginobil
PG Neal
With Green used as depth at the wing and Mills used if Neal goes cold.