This derailleur isn't quite toast yet. But the decision whether to save it rests on the availability of a suitable replacement. If there is one, just buy it.

However, if there's nothing decently comparable, drill out the head on the rivet on the lower arm (the one with the spring). Push out the pin, and slide the spring off. Scavenge the junk derailleur bin, for one with the same spring (Shimano probably uses the same spring on a number of FDs). Rebuild FD with new (used) spring, using a screw and nut in lieu of the riveted lower pivot pin. Either use Loctite or distort the threads so nut doesn't work loose.