A recipe calls for pomegranate molasses. What can I substitute or can it be left out entirely?

I've used this Hibiscus Simple Syrup as a substitute for pomegranate molasses in many recipes and I've always liked the results. It's very easy to make and lasts quite a while refrigerated.
Bring to a boil
1cup water
Add
2 cups sugar or Splenda
Reduce to low heat and stir until dissolved
Add
2 handfuls of dried hibiscus blossoms
Stir well, and simmer for 15 minutes.
Cool. Strain and discard blossoms
Transfer to a jar and keep refrigerated.
It's amazing in cocktail recipes, iced tea, berry sauces,

I also suggest getting the pomegranate molasses. Its flavor adds authenticity to the dish and if you make Turkish or Middle Eastern recipes, you will find many uses for it. Earlier this week I added a tablespoon to a salad that I dressed with olive oil and a bit of balsamic. The salad was was delicious.

All good advice, but especially susan g's note that pomegranate molasses can be inexpensive and keeps really well. If you can find some, why not go ahead and get it? I once brought a bottle to a friend's house when I'd been tasked with making a dinner for his weekend house party. I only needed that tablespoon or so, but I brought a bottle and left it with him. A few weeks later, I got a note thanking me for the pomegranate molasses--he'd been using it in everything and absolutely loved it. A better house gift than whatever it was that I'd brought intending to be the gift!

I did this just the other day, for a Turkish lamb and apples stew that called for 1 Tbls pomegranate molasses. I substituted 1 tsp regular molasses and most of the juice from 1 lemon. It isn't the same flavor, but it will maintain the sour-sweetness balance.

I buy it in an Indian store, where it's inexpensive. It keeps very, very well.
I've seen salad dressings using it. I first got it to make a Middle Eastern dip -- http://www.theperfectpantry.com/2008/03/aleppo-pepper.html

If you're going through the effort to make something with such a specific ingredient it is probably worth the cost of buying it just for this dish.

Any recipe that calls for tamarind, works well with the molasses, (works for Indian recipe definitely)

you could make your own molasses, just buy a bottle of the juice (with no additives & flavors) and reduce it down to a srup by boiling it in a wide saucepan..

That was my thought as well, but I didn't want to buy a one-time use ingredient. What else could I use it in?

You might be able to use a high quality balsamic vinegar, but nothing really approaches the flavor.