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human
[MCU] Did Loki know he would die trying to assassinate Thanos?

The whole scene seemed very final. I'm not sure if this was just cinematic effect or if Loki actually knew he would die trying to kill Thanos. If that were the case, why would he try it anyway? 

In addition, Loki is a god of mischief and trickery with thousands of years of experience, was access to powerful illusion magic. You'd think he would come up with a better lie than, "I pledge to you my undying fidelity." And you'd think he would send in a clone to do it instead of going in himself, just in case Thanos saw through the lie.
gpt
At that point Thanos has the space stone, the only source of Bifrost is dead, Thor is captured, and Loki likely doesn't believe he's ever going to get another shot at killing Thanos.  He knows his odds of success aren't high (Thanos just manhandled Thor and Hulk, the two things Loki is most afraid of in the universe), but he appears to sincerely believe he has a shot at killing Thanos. 

As for the speech, Loki sweet talked his way into Thanos' good graces once, to the point where he was given an Infinity Stone and an army.  He likely used very similar lines, poking the Mad Titan's ego to get him to let his guard down.  One of Loki's recurring flaws is trying the same trick twice (or apparently dozens of times in Thor's case) and assuming it'll work every time. 

Loki could have sent a clone or an illusion, but the chances of success would have been lower and the cost of failure would have been essentially the same.  Loki probably can't survive in the vacuum of space as well as Thor can, and Loki knows how vengeful a person Thanos is.