It all depends on how you maintain your car. Regular, preventive / periodic maintenance is the key for trouble free car, and if you forsee any problem; just go for proactive approach and immediately rectify the problem.
Just as a rough guess, Well maintained Vitz should easily run trouble free for at least 150,000 Kms (with minor replacements of normal parts and if required, like belts, wheel bearings, brake pads, engine coolant, brakes fluid, etc.)