Loki at the time of Thor 1 isn't far gone enough to consider killing Odin. He wants Odin's approval. He can't get that if Odin is dead.
Even if he tried to kill him I don't see him getting past Hiemdall or Frigga to do it.
When Odin wakes he is going to find his son dead, the Jotuns dead and Earth taken over.
Loki will have some explaining to do.