I'm not sure how another pump running would work. Wouldn't you have to throttle back the main so that 2 working at the same time wouldn't overload your overflow? In other words, a second pump will increase the return water flow, right?
What's the reason for your paranoia about it stopping on you?
One thing I would recommend to anyone is to have another pump impeller on hand. Of course, that doesn't help going out of town concern. My impeller cracked once and I had to wait for overnight delivery to get another. In the meantime, all in my sump/fuge died of course.
"Life may not be the party we hoped for but while we are here we might as well dance!"