Mears lost my bag while I was using the Magical Express back to the airport last month. I'll walk to my resort before I give their company anymore business. Heed this warning - Mears operates some taxi's that are at MCO. Good luck and I hope you have fun.
Do you mean you had your bag with you and then it was loaded onto the bus and then wasn't there when you got to the airport?
Or do you mean you used Resort Airline Check-in in your resort's lobby, where you checked-in for your flight, got your boarding passes, and checked your bags through to your home airport?
If you used Resort Airline Check-in, then Mears had NOTHING to do with your checked bags. Mears does not run all of Disney's Magical Express. They are a subcontractor, one of about 5 subcontractors. Mears' role is supplying the buses and bus drivers. Disney is in charge of the entire operation ... Mears and the other subcontractors merely fill their roles.
If you used Resort Airline Check-in and your bag was lost (was it truly lost forever, or merely delayed???), then the fault lies with BAGS Inc., the Resort Airline Check-in subcontractor. BAGS Inc. employees accept the bags at the RAC desk in the resort, BAGS Inc. employees drive the luggage delivery trucks, and BAGS Inc. employees handoff the luggage from their custody to the custody of your airline.
I have no love for Mears, but I just thought it was important to set the record straight, and to make sure you're annoyed with the right company.
And actually, since Disney is in-charge and Disney sets all of the policies and procedures for everything its subcontractors do, then the ultimate fault lies with Disney.
Of course, if you used RAC and your AIRLINE delayed your bag after they got it, then your beef is with your airline.