It's hard to see the TT droop you mention. Perhaps a shot with the straight edge placed on the tune to see the gap? Also how's the DT and fork? There doesn't look to be any buckling so I doubt any structural issues exist. If the bike had a directly frontal impact there should be no twist to the HT and only a rearward bending. Sighting along the HT and ST might indicate any twist. If the head angle was moved back due to an impact then the steering geometry has changed. Whether it's changed much and to the negative with a loaded bike a test ride will give the truest finding. Also the fork might have been bent in an impact. Fork twist is easy to spot with a couple of straight edges. Side to side off centering a bit harder but a good wheel and sighting down along the steerer past the mounted wheel can bring out this potential. The fork's possibly being bent back is best looked for by supporting the steer off a surface with the blades curving up and then rotate the fork with the blades curving down (and hanging off the surface edge). Measuring up from the surface to the blades' point before thety start to curve should be the same both ways the fork is set.

How any slight bend/misalignment effects the ride/stability is a tricky thing until you test a built up bike with touring weight loaded. I have known a few bikes with slight impacts that improved their stability and many that negatively changed things.

But don't think that the bike was built with perfectly straight tubes, or the after brazed up frame had straight tubes after aligning was done at the factory. Measure to understand but test to be sure of real world results. Andy.