When Sulla marched on Rome, he basically broke a taboo that had endured up until this point. Now that someone had marched on Rome, already, it now became a real possibility for others to do.
So what if Marius caved in, or died prior to the escalation that lead to Sulla marching on Rome, and Sulla doesn't march on the city and gets his command against Mithridates.
Short term implications are easy: No proscriptions, no sullan reforms, Pompey has to pursue a conventional career, crassus doesn't get extremely rich. Sertorius doesn't fleet to Spain, etc.
What are the long term implications of this though?