I am considering DME-LHR part of a multi-segment trip. I am prepared to pay for Biz but only if I get a widebody service. Currently there's a 787 scheduled for "my" flight but it seems BA also serve DME with an A319/20. How likely is it that the flight gets "downgraded" from 787 to 320 and what recourse do I have if it happens? Does BA usually offer rebooking (on other carriers as well?) or compensation? Or is it just tough luck?