I don't know how to evaluate "certain enough" for you.

I can tell you, however, that over the course of any given year, Delta offers tons of SkyMiles dining bonuses, while NW offers none outright (instead only qualifies dines to earn 5 points in their frequent point-colleciton-based bonus programs).

So if you only use SkyMiles Dining when they have bonuses, you still may get all the way to enough Delta miles just through dining during those bonus periods to get an award (which you can then redeem on NW if the merger happens not to go through).

And Delta offers other kinds of bonuses too. So much so that, in one year, I earned 45k Delta miles just by jumping on bonuses which were too good to pass up even though it's not my first choice or second choice or third choice or fourth choice or even fifth choice airline to collect with! 4000 bonus miles for joining through Starwood last summer, several thousand for getting a Delta Amex with no annual fee the first year, 1000 miles per car rentals during a few promo periods, etc. But sitll, a lot of those 45k miles were from their dining bonuses over the past year.

So that'll add to my 140k or so NW miles assuming the merger goes through. But just in case it doesn't, it more than enough to use a number of different ways.

And, btw, keep in mind that, assuming the merger goes through, which is still months away at least, it'll then likely take them a year or more after that before they can merge the FF programs. So they still may have separate bonus approaches all that time.