If everyone converts to Islam who are they going to kill?
If every one converts, then it will become a matter of which sect - Shia or Sunni - will come out on top.
The killing will continue until one or the other is supreme.
If the Sunni win, then they will kill each other until one or another cleric’s views are supreme and there is no dissent.
Should the Shia win, then it will be a matter of which sect inside the Shia sect wins by killing all the others.
If the 12ver Shia sect wins then they are obligated to bring what remains of the human race to paradise ... that done, the last two must kill each other ...
Does that answer your question?
Each other, same as always.
When the last two people on earth are muslims, Achemed'll slay Ackbar for not being muslim enough.
Each other as they do now in their own countries. Wish they would hurry up.