Here's my plan:
First: Play out the remainder of the season with the current roster. As currently constructed, this team should make the playoffs and finally get the OKC draft debt off the books.
Second: Spread things out in free agency...
1. Keep the German around - Dirk for $12mil
2. Shore up C - Gortat for $9mil
3. Replace Marion - Ariza for $8mil
4. Split up the Ellis/Calderon combo - Outbid Indy with $11mil for Lance Stevenson
Here's how the roster would look ($68mil total salary - approximately equal to this year's):
PG: Calderon ($7mil) / Larkin ($2mil) / Mekel ($1mil)
SG: Stevenson ($11mil) / Ellis ($8mil)
SF: Ariza ($8mil) / Crowder ($1mil)/ Ledo ($1mil)
PF: Nowitzki ($12mil) / Wright ($5mil)
C: Gortat (9mil) / Dalembert ($3mil)
The roster above is incredibly versatile and flexible from a trade standpoint (with the inclusion of a draft pick the Mavs would finally have control over) if the right opportunity presented itself mid-season.