Fellow UR student here.
First of all, plenty of students rush here as sophomores (or later). His chances of being in a frat are not over for good.
Second, at UR frats don’t determine your friends really. His friends he made won’t abandon him because he’s not in their frat. The frats aren’t exclusive in that way. Heck, people who join different frats are still friends. This is different than a lot of schools, especially because there are no fraternity houses. Students in Greek life live in the dorms. The lodges are only used for the fraternity meetings and parties.
And there are plenty of things to do on campus if you’re not involved with Greek life! Plus, he can always go to the frat parties (he doesn’t have to be in one to go).