bmi baby and regional pilots being integrated is never going to happen. Sorry.
Also CR is very unlikely, I'm sure 3800 pilots can absorb a surplus easily with voluntary measures, esp with a lot of over 55s and 60s in both airlines.
The only downside for DEPs waiting is that you've just lost 300 seniority places overnight. The good news is these extra slot pairs means you actually haven't lost anything as the airline is expanding, and as someone said in the long term there will be even more expansion as these slots are converted to LH.