My $0.02:
I personally only would consider deferring if I commuted, and all my financial needs could be met on FO guarantee. Commuting to reserve $ucks big time, and you can probably make up some of the pay difference by being a senior bidder (also kids & Xmas off = priceless).
If you’re worried about a merger, ALPA merger policy isn’t PIP insurance, and will not guarantee your seat.