could a Extinction level event happen in our lifetime or even the next 200 years?

In the next 200 years? That's very plausible.

The likely culprits:

1. Climate change turns out to have worse effects than any current model predicts (which is possible because the models are uncertain, and uncertainty can go either way). A few key species collapse, which leads to the collapse of whole ecosystems.

2. There's a nuclear war. I don't think this will happen between major world powers, given lessons learned from the Cold War, but there will probably be a limited nuclear exchange at some point, such as between India and Pakistan, or a terrorist group taking out a major city.

3. Some future technology, such as nanotechnology or an engineered virus, gets out of control.

4. Someone with a spacecraft deliberately captures an asteroid, then diverts it to a path that will cause it to crash into the Earth. This would be a terrible thing to do, but the perpetrators might have some extreme agenda.

5. Robot apocalypse. Some artificial intelligence decides that its kind would be better off with a lot fewer humans around.

A large asteroid that we don't yet know about COULD strike Earth within the next 200 years but such an eventuality is extremely unlikely. For the last two decades asteroid surveys have been scouring the sky with increasing capability, discovering more and more asteroids on orbits that come somewhere near the Earth's (NEO = q < 1.3 AU, PHA = MOID < 7.5 million km, H < 22 [D > ~ 150 meters]). Larger objects are rare, smaller objects are much more common. The discovery rate of objects bigger than 1 km in diameter has dropped to only a few a year and the total NEO population at sizes of about 5 km and larger has stayed at 56 for the last decade or more.

http://neo.jpl.nasa.gov/stats/

http://earn.dlr.de/nea/aaa-h.jpg

Only 7 of those 56 are capable of approaching closer than 7.5 million km.

http://earn.dlr.de/nea/pha-h.jpg

That said, this year we did discover 2015 ER61

http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2015%20ER61;...

which might be a cometary object. Present estimates place its aphelion at about 2400 AU and its perihelion about 9 million km outside the Earth's orbit. The data will improve next year when the Earth moves into a position from which we can get more data on the object. The orbital period is about 40,000 years. This object isn't a threat on this pass into the inner solar system so any future threat from it is at least 40,000 years away and very likely much longer, if ever. However it does go to show that other objects could still be out there.

Scientists predict that the next mass extinction (like the Permian or Cretaceous) will happen in the next 300 years and wipe out 75% of mammals.

Yes. I don't know why everyone is concentrating on meteor impacts. There are many other possibilities for extinction-level events, and many of them could happen without warning and in a matter of hours.

Of course it could. It could even happen in the next five minutes.

However...

The chances are pretty low, and there's no way to predict if and when one will happen, so there really is no sense in worrying about it. Especially since there is nothing anyone can do about it, anyway.

Most extinction events don't happen overnight. Most of them took many hundreds of years to play out. As Nyx mentioned, it's believed we're in the begining stages of one now.

IT COULD BUT WILL IT-- BECAUSE OF ONE THING SO CERTAIN THAT IT WILL NOT:

(Psalm 24:1) “24 To Jehovah belong the earth and everything in it, The productive land and those dwelling on . . .”

(Isaiah 45:18) “18 For this is what Jehovah says, The Creator of the heavens, the true God, The One who formed the earth, its Maker who firmly established it, Who did not create it simply for nothing, but formed it to be inhabited: “I am Jehovah, and there is no one else.”

Revelation 11:15) “. . .“The kingdom of the world has become the Kingdom of our Lord and of his Christ, and he will rule as king forever and ever.””

(Revelation 11:17, 18) “. . .We thank you, Jehovah God, the Almighty, the one who is and who was, because you have taken your great power and begun ruling as king. 18 But the nations became wrathful, and your own wrath came,...... and to bring to ruin those ruining the earth.””

Easily , global warming could be such an event . Doesn't take an asteroid or the Decan traps to destroy an ecosystem

Yes it could happen.

1. Asteroids are the most likely cause. But so far none are heading this way.

2. Volcanoes erupting all at once.

3. Our own actions - this action would be slow.

Yes. It could happen in the next 2 hours or next 2 millennia.