I am sorry you're being put through this stress!
I believe that UPS dropped the ball here and for whatever reason, they got careless. From personal experience, whenever UPS or FED EX, etc. messes up, it's almost always because the regular route person was out on vacation or had a sick day. Those temporary substitutes are often not given enough instructions or tips on what might be necessary to successfully deliver in your particular area. Or worse yet, if it's someone's first day or two on the job, they're bound to make errors.
I am in no way excusing anything they did wrong. But the Good News (?) is that I am confident that Coach will make it right. You've already spoken with your SA's coworker who told you that your SA will contact UPS. It is totally Coach's responsibility to ensure that you get your package. On top of that, Coach was careless in not updating your package's ETA, which your SA will take into account.
As aggravating as this must be for you, Coach WILL take this matter into their own hands, as UPS has to answer to Coach -- who is their client -- and a valued one, at that! Hopefully this will all be just a simple SNAFU that will end up with your 'poor bag' having been driven around needlessly without being discovered by the right employee.
If you were dealing with some fly-by-night company that you'd never heard of before, I would be worried. (Not that you'd order from a shady company in the first place).
Be sure to keep us updated -- you have nothing to worry about (except a little wasted time)! You've probably guessed that I've had similar PIA experiences -- not with Coach, but other big name retailers.
Good luck!