Simon Mason wrote:
...............
The next night I went out for a 20-mile run, but my confidence was
shot; I was convinced that I was going to fall off at every bend.

Bad luck with the crash. I know exactly what that feeling is like but
confidence will gradually return to 97% of what it was before too long.
That little bit of extra caution will do you good when it comes to dealing
with wet and icy bends. Oil is terribly lethal though: there's not a lot
you can do about it apart from riding at under 5mph all the time - so,
really, we have to take our chances with it. Fortunately, oil/diesel
patches slippery enough on bends in just the "right" places are very few
and far between. I've only ever slipped over on oil once: very scary and
painful. Skidding on it on the straight is just as scary but quite fun
once you realise you're still upright and in one piece :-)

Also
my rear derailleur must have been damaged, as I could not get the 6th
and 7th cog on the rear cassette.

Frame's gear hanger might be bent (can be straightened if integral steel
type). That's more common than damaged mechs.

~PB