The Suns record over the last eight seasons without Nash is something like 10-25. The last Suns team that did not have Nash for a whole season went 29-53. That team featured two All-Stars (Marbury, Marion) and two future All-Stars (JJ, Stoudemire) before Marbury was traded and Amare was injured. We currently have no one even close to that talent level on our team.
This could end up being a historic season for the Suns. They have not lost 60 games in a single season since their inaugural season. Of course it is possible the team will somehow overachieve, take everyone buy surprise, and muster 42 or so wins for a final playoff spot. It's possible. Just not very likely, imo.
The Suns will probably finish around 12th in the West, but could move up a couple spots if some other teams struggle.