... When BA took over BCal I believe they took the crews and integrated the seniority list, but when Dan-Air was bought out (bar the 737 guys) everyone was made redundant.
After the takeover of Cityflyer quite a few years ago the pilots were intergrated into BA (bottom of list, grandfather rights to command etc). However some pilots were found not to be to BA standards and it was decided that in future ALL pilots would go through selection before joining mainline.
So... anything could happen - whatever suits BA at the time