There will definitely be quite a bit of lay-offs. Cost savings are probably the biggest driver behind mergers, and guess what the biggest piece of cost pie is? Overlapping positions will be gone, who needs two CEOs, CFOs? ect. Rite-aid side will summer more. There will definitely be quite a few store closures, as former competitors across the street no longer make sense.
But financially, the bigger Walgreens will likely be in a stronger position. So from an impartial 3rd person perspective, I can see the merits. Changes, favorable to you personally or not, is constant and unavoidable. Adapting to change or even ride it, putting up a safety net or preparing alternative solutions are as much a part of a successful career as good lucks and prayers.