I can't NOT speak from experience, but I can speak from what I've read...
From my understanding, the main purpose of the ME mail is the tags. So if you are late in getting ME booked (or miss it completely), you can still take ME, but you'll have to collect your own luggage. The ME tags are to be put on your bags and a CM will get your bags for you.
Personally, sit back and enjoy the excitement of your upcoming trip. (Oh, trust me, I know it's much easier said than done.)
You'll get everything worked through. But try to get ME on the phone today to let them know you'll be arriving.
But don't worry if you never get an ME packet ... just collect your luggage yourself and the CMs at the ME check-in can verify your information.
I just recently read a TR where the family forgot their ME mail with the vouchers. NO ISSUES! They got on ME just fine.