Direct swap to BA for me. My flying patterns were mostly on BD - domestic flights interspersed with the occasional exotic adventure to somewhere in C class for Y mileage - so it's an easy switch.
The only change in my patterns will be in my foreign leisure trips: the loss of C-class-for-Y-mileage and the gain of many more direct European routes with reasonable Y prices mean it's probably goodbye to the likes TBS, BEY, DME and CAI and hello to some 'new' places - possibly LIS, DBV, ALC or PMI.
Nobody except BA has made any attempt to capture my business (and even if they did, the mileage thievery of M&M and Flying Blue would put me off considering a switch to eg LH/LX for Europe or Cityjet for Edinburgh).