Whatever your new pads are, you shouldn't install only on one side, as the friction coefficient could be different from the other side and cause a pull.
New pads on well used rotors aren't a great idea-- yeah, they'll eventually conform to the grooves and work ok. The "rules" about "pad slaps" apply.
But if your other rotor is decent, yeah, leave it if you need the money.
Whatever the reason you went metal on metal should be addressed, if it was a sticky caliper or sticky pins. If you have sticky pins on one side you should clean and lube the other as well.