RE: Wing Spar
That main spar looks awful thin for a plane that size.... You'd think it would be metal...
Easy to fix if you wanted to open it up abit but I doubt you want to do that....
You could sand the remaining bit to a clean end and jusat insert ito the other wing as usual as it's not strucutral and there is enough to assist the bolts in anti-rotation.
What I would do:
ON the remaing bit, clean up the end... cut a slot into it... make a mating piece.... epoxy and be done.