I forgot to pick up Red Wine yesterday when I went into town! Can I substitute a good merlot?

dymnyno's answer is beautiful, and typically informative. On the soft side, I'd say use anything that doesn't require another trip to town.

I just made a similar short rib ragu (for 50 people) and I used some merlot , cab franc as well as Cabernet. (left overs from our tastings) They are varietals of wine that are used in a Bordeaux blend and will work well in the sauce.