No worries pp. I'm not sure it's 100% yet! but I'm going to whack a new mech on and see what's what.
You did a bloody good job of getting that beauty straight again!
I would say mine was about half as bad as that, in all directions. I.e. Half as far rearward and half as far over the cassette.
I basically made sure that the axle was nicely clamped in the bottom of the dropout with the qr. Then turned the bike upside down and pulled it out first then forward, bracing the frame against my leg. Wrench over the top of the hanger, on as far as possible. Nice long pulls and constant checking by eye. I then made sure I just over-closed the dropout slightly to then ease it back out a mite.
The thing I can't visualise is the fore/aft position of the hanger pre-incident. My guess is that if the dropout is now roughly the same width as it was, and the same width down the slot, then that is the best I can do.
The only other thing I have thought of is sticking a dowel of nearly the right diameter through the mech mounting hole to see if this gives any inkling about straightness.
If you have any top tips I'd be glad to hear them. The adjustability of a rear mech (high low limits and b tension) should be enough to compensate for any inaccuracy on my part - so long as it is square to the sprockets and forward enough to ensure the chain has enough 'wrap' on them?
Or at least that's the theory! Seriously, though if you do have any nuggets of information I'm always keen to hear about them. I love a fix or a bodge!