I think it's still open, it always looks like that when I pass by, which is quite often. I had their Brooklyn Style Pizza when they first opened, I had it delivered. The delivery person was sharply dressed which impressed me more than the pizza. We also sampled their cheesesteak which was a definite miss. A few months later, I called again for delivery, hopefully to get a second opinion and was told they couldn't deliver because they were too busy.
I've wanted to try dining in, but felt I'd be the only one there which I find quite awkward.
We just drove by Grandma's Grotto about 10 pm and I am happy to report that they are still open. This place never seems to be crowded but the food is good. They are a nice couple that moved their family from Staten Island, NY to Horsham because they thought it would be a better place for their children. I hope they can make it.