For one thing, the universe has been around forever.
This means if any antimattter out there hasn't collided with matter yet, it's probably not going to collide with it tomorrow either.
Some of it got away, it was no big thing, same ole same ole.
It doesn't all come at once in one universal energy decay event, the universe is too big for that, there's no limit to the universe, it's infinite with infinite energy. Energy is always conserved that way.
This means if any antimattter out there hasn't collided with matter yet, it's probably not going to collide with it tomorrow either.
How long has the universe existed? How long, to the best of your knowledge, has plutonium existed? See a pattern here? Of course not, that was a leading question. I seen on TV show some of top nucular science wizards in manhattan were worried that a a u-bomb might actually set fire to the atmosphere. Boy that would suck, eh?