Yep. Triple therapy is now standard in HIV treatment. The odds of developing mutations to 2-3 agents simultaneously are very low

When I was a teenager, I wrote a connect four game, and my brother would play it. Every time he'd win, I'd jump back into the code. I realized it was a fruitless cat and mouse (not only because the game is trivial) but because of the pacing of my "fixes" -- if I could have had the final version completed before he first played, he might have been stymied, but the iterations seemed to give him an easy path -- he only needed to solve one problem at a time.

Why don't we deliver all antibiotics as a triple? Wouldn't that eliminate antiobiotic resistance?

Antibiotics kill bacteria, not viruses. And that includes desired strains.