For mono - worst enemy is heat and sunlight. If not used often and kept in a shaded / cool area - you can get few seasons from it.
Braid holds up very well. I changed out some reels and a friend took my old braid. He uses it about 15 times a season - that was about 10 years ago.
Keep in mind - the lighter the test - more often you should change it. You lose 50% strength on 80lb - still good chance to land a fish.
Lose 50% on 12 lb - now it's only 6 lb test.
Another tip - often the knot fails long before the line breaks. It pays to cut off knots and re tie them often.
What could be more mundane than dying of old age or of natural causes when there is death by misadventure to be pursued ? Skip