I second what Muirenn said. If you otherwise know the route, show up and see what happens. If they do ride in a paceline, then you might want to stay to the rear anyway and just watch how the group functions. If you can't keep up, you can't keep up. No sweat. Just make sure you know how to get back to your car.
FWIW, I did a local club training ride weekly for a few years. The group was well used to new riders (either new in general or new to the group) not keeping up at first. Those that stuck with it soon could and showed significant gains in their speed over time. We did ride in a paceline, and it is a skill that involves some risk. If this is a paceline group, I would keep some extra distance between you and the other riders. If you do a search here or on roadbikereview's site, you will find some past threads on it with some important pointers for paceline riding.
I grew a bit weary ulimately of it. Some groups are just better than others, and I preferred ultimately to ride with friends. We still kept up a decent pace and rode in a paceline, but it was more relaxed.
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher