Sorry to hear about Andy.
There is no doubt that the risk of a crash is higher riding in a paceline. No matter how safe you try to be, and follow all the rules on how to do it, your odds of a bicycle to bicycle collision are higher riding in a pace line than riding solo.
Anyone that's spent much time riding with groups, or just watching professional bike races has observed that.
You can reduce the risk by riding with better riders, and working on being safe and predictable yourself. Good technique reduces but doesn't eliminate the risk. Even Pro's crash occasionally riding in a group.
On the countervailing side, I strongly believe, admittedly without quantative data, and setting aside the example of Andy, you're much less likely to be hit by a car riding with a group, just from safety in numbers,law of averages, and visibility.
So IMHO, your odds of a crash go up riding in a paceline, but your odds of death from collision with a car go down.
Also, you have to factor in the fun of riding with a group and what that benefit is worth to you.
Applying this to your situation, I think you have to make an honest assessment of the risk of a second head injury that you're willing to accept, and your own riding skills, and ability to perceive and react.
__________________
You could fall off a cliff and die.
You could get lost and die.
You could hit a tree and die.
OR YOU COULD STAY HOME AND FALL OFF THE COUCH AND DIE.