Brazing is strong (stronger than solder). This is why HVAC systems are to be brazed vs. soldered. They typically run at higher pressures than say a water supply (R-410a can see pressures of 300+ psi). The other issue is vibration, etc. that could weaken the joint.
How long it will last is anyone's guess. The repair may hold fine, but the question is that whatever caused it to leak may cause it to leak again somewhere else. If it leaks again, then it is just a matter of how large the leak is. If it is small, the system could be topped off every year or 2 (or whatever). It is expected that the price of R22 will increase over the years and you will reach a point where it will be better to replace vs. repair/refill.