OK to ride with a slightly bent mech hanger?
Derailleur hangers are supposed to be, to some degree, a component that bends to save the derailleur. The hanger on one of my bikes seems to get bent at the slightest impact. I'm considering ordering a spare and carrying it around in my tool kit.

If the indexing was severely affected by the fall (moving inboard a whole sprocket definitely counts as 'severe'), you need to address the problem properly. A bent hanger is going to affect shifting and put extra strain on the chain, and you risk the cage hitting the spokes when changing to the largest sprocket.

You can eyeball the derailleur cage alignment by looking down the chain-line from the back of the bike - see image below from this question. The derailleur cage should appear to be parallel to the chainrings.

My LBS only charges $20 for hanger alignment and indexing adjustment (I'm in the USA). Worth it to get the hanger straight and avoid associated problems.