BITD, when I rode rather more hard-core than I do today, we regarded light aluminum bars (defined as anything under 170g for quality straight bars of the day) as 1 season only bars. We regarded 150g as the lightest practical bars for normal users. Some manufacturers offered lighter ones, but they were never intended for long-term use, Syncros for one said as much.
Now, knowing that a bar should be replaced annually under hard riding didn't make it happen. I broke 3 or 4 bars over the years, excluding bar-end caused failures. All of them failed near the stem clamp, and all of them failed somewhat slowly, first buckling and bending. None simply snapped catastrophically.
In '98 I switched to a Profile carbon straight bar, it came with an "unconditional lifetime warranty", which I exercised 2 times, both times when bar end clamps damaged the ends of the bar in a crash. The carbon bar itself hasn't ever failed me. The on on the bike now has been there for 14 years, including a year or 2 of pretty rugged use, and many more effectively languishing in the basement.
Aluminum bars absolutely will fail in extended service, just as an alumimum frame, stem, seatpost or aircraft will eventually fail. Aluminum has a finite fatigue life. That means that any cyclic load, even well below its load carrying ability, will eventually cause a fatigue failure. A crack will begin, it will spread, the part will fail. This is why a low-end steel frame typically carries a lifetime warranty, but alu frames, no matter the quality, get 5 year warranties from most makers.
Aluminum structures are built for a certian life expectancy. Most alu frames will outlive their owner's need, but some fraction will fatigue in service. 150 gram bars have a very finite fatigue life, and any regular mountain biker would be wise to replace them annually. On a cruiser or dedicated trundle-about-road-bike, the same bar might last 20 years.
So, just like the aluminum frame, the bar deserves a careful checking over every few months. Any sign of a crack should be checked carefully. Any crack identified is terminal to the piece, and it should be replaced post-haste.