I would cold bend it; heating would anneal (reduce hardness) the steel. If it's only been bent once or twice, straightening it shouldn't be a problem, just be careful not to overshoot and bend it back and forth repeatedly as each cold bend will harden/fatigue the steel a little more. The good thing about FOMOGO's method is that it works both tubes together, keeping them even, but you could do them individually by sliding a larger tube over the fork tube to concentrate the bending force where you need it (if you just pull on the fork tube, it will tend to bend in another area rather than straightening the existing bend). If you can weld, or have a welder nearby, there are a few ways to reinforce the fork. You could cut the flattened ends off and slide a smaller tube inside or a larger tube outside, then weld the end back on (and weld the ends of outer tube if that's the way you go). Another option would be to add a "bridge" to the front or rear of the fork tubes (rear would look better, IMO, but may restrict steering). As for seeing cracks before something breaks, the black paint would make that difficult, but you could remove the paint and inspect the bent areas, just avoid removing metal with the paint (use paint remover or hand-sand) as you don't want to thin/weaken the tubes. Of course, if the fork is super-strong/rigid and someone runs the DB into a tree or other solid object, the frame would probably bend instead of the fork, but that may be the least of your problems in that situation (Helmet!). I tend to overthink things, so I'll add that just straightening the tubes and inspecting afterward would probably do.
Here's one idea for a bridge design, the triangulation should add a lot of strength.