Not sure how feasible that would be. All paint etc would have to be removed for welding that area.Take the vehicle to a shop. Have them temporarily tack weld the striker in place and check to see if the tailgate latches. If eveything lines up ok finish welding it in place. Was the vehicle in an accident?
A plate could be fabricated spanning both holes , drilled and tapped for bolts. Could possible even be out of aluminum . Then just getting in place the next challenge