Rendon has been injury prone since we got him. I think Upton would deliver as much offensively as Rendon potentially could.
The only problem that leaves us is at first base next year. I would be fine for keeping them too but if this offer was on the table, I'd do it.
The obvious answer would be to pick up Adam LaRoche's option year and go with a platoon of LaRoche/Moore platoon at 1B then go Harper/Werth/Upton in the outfield.