My adopted cats were indoor cats (say I, since both were declawed) who were both picked up as strays by my county's animal control...no chips, no collars, both approximately 3 years old. My boy still tries to door dash, and has actually gotten into the condo courtyard twice....I am thrilled that he now has a chip, since the collar and tags they both wear could come off (breakaway collars). That particular shelter chips every animal that comes through that's adoptable. Granted, not everyone will think about chips, but all the police in my area have the scanners for the major types of chips, as do the vets.
My vet scans every check-up to make sure the chip hasn't migrated - apparently it's extremely rare, but can happen. I've also talked to a few vets, who all said the benefits of the chip far far outweigh any possible downside. Life is always a gamble, but this risk seems fairly minimal, compared to having a lost cat. I don't think there's a person in the world who can guarantee their pet won't get into the 'out'.
Personally, I think you did the prudent thing to safeguard your cat as much as possible. Don't forget to complete the registry of your cat with the chip company. And don't forget to update info if you move. People do forget.