What would you do?

At some point, you can affect everything so much that you're never born. So, oops, there ya go.

However, the very act of being there is, for sure, a change to the timeline. You weren't there before. You weren't there to eat the last leg of mutton or catch the fair damsel's eye, or stand in front of someone on a field of battle (and get the cannonball meant for them), or even take up time in the outhouse.

This is an issue with much of time travel fiction: there's some idea out there that all changes will be grand and obvious. But a lot of them probably wouldn't be (kudos to Ray Bradbury and The Sound of Thunder).

What happens if you, the time traveler, leave a footprint on someone's property, and they thereby get angry at someone other than you and start a feud? Feuds have been started over less. What happens when your unusual hat distracts someone long enough that they stay in the crosswalk an extra 2 seconds and are hit by a bus?

destroy humanity

If this topic interests you try reading Stephen King's 11.22.63 - by the title you can see it is about traveling back in time to prevent JFK assignation. But other things happen which impact potential future --

Or, watch The Simpsons' treatment of The Sound of Thunder in "Treehouse of Horror V" (season 6, episode 6, Time and Punishment, second short story).

Having to live 7000 years??? Why can I not kill myself upon arrival?

Silent observer.

At what point can one simply observe?