What if Thor was not banished by Odin? Thor would be crowned king, but Loki would attempt to disrupt the ceremony one last time. Thor would have already been declared king of Asgard. Thor would find the Frost Giants, and kill them. Thor would then declare an all out war against the Frost Giants. He would take Asgard's army and attack Laufey.
Remembering that the last time they fought Asgard, they lost, the frost giants, with the help of Loki, would travel to the remaining realms, requesting, and sometimes forcing, the other realms armies to stand by the Giants side. Out of arrogance, Thor stated that Asgard needed no backup, and that the Frost Giants were cowards for getting other armies.
The battle would begin, and many would be slain. Soon, Asgard understood that this battle was Ragnarok, the end of the 9 realms. Thor would keep fighting along side the other gods, while the army of Asgard fled the battleground. The battle would destroy the realm they were fighting on. Soon, Asgard would be the only realm left alive. Asgard would fall, and be destroyed like the others. Thor's arrogance would bring the end of days upon us.
This is what would happen if Thor had not been banished by Odin.Don't forget requests for future articles!