Am I being complacent thinking it’s not going to matter – LBS has none in stock – could I leave it or wrap some wire around recessed end of pad bar ? Pad bar is threaded so surely it’ll just stay in place without snap ring ?

It’s just for added security. A wee dab of Loctite might give you piece of mind.

both mine have fallen off, I just make sure they’re nipped up tight. Wouldn’t use loctite after needing a new motorbike caliper due to loctite well and truly sticking a pad pin.