One of the torsion springs on our garage door mechanism broke, the door
closed with a bang, and the idler sprocket (plastic of some kind)
shattered into pieces.

I have already read a warning that trying to replace one of these
torsion springs can result in injury or death, so we'll have to call
someone.

The question is: to what extent are the torsion spring mechanism and the
opener interrelated? It's an old All-O-Matic opener (installed by a
previous owner) with no optical sensor to prevent injury to people who
happen to be in the doorway when it closes (although it does reverse if
it meets a physical obstruction). There is also no way of opening it
just a little way (e.g., to get the newspaper) then closing it again
without first opening it all the way.

So if we want to install a more modern opener soon anyway, do we still
have to have this spring replaced first, or do we need to think about a
whole new mechanism, perhaps of a different type?

Perce