No, I don't want any character to die. And No, I don't want Imu to be the winner. I undertand the art of "being saved by the plot" if it's done in a good way. As long as the villain look good and is never stopped by the main character, but others circunstances, I don't have a problem with that.
Look at Luffy escape in Marine Ford for example. 3 admirals couldn't stop him, but Oda never drew Luffy dealing with them, it was just a bunch of powerful characters assisting Luffy and stalling them, no defeating them. (Unlike the Lorosei in Egghead that were Luffy' and everyone's punching bags, and they were unable to launch some attacks against anyone)
What you suggest is that Luffy himself with Loki are able to stall Imu, nah, that's not tension... nobody will take Imu seriously that way.
I agree on the time limit thing, but Oda need to sell on the perception that Loki and Luffy are about to lose/die.