If you make a Sheva Brachos meal for a new Chosson and Kallah and your Panim Chadashos (new person) does not show up, can you still say the Sheva Brachos?
The Gemara Ketubot (8a) states that after the first day, Rav Ashei would only recite the sheva berakhot if there was someone new. The implication is that it is a complete requirement, and no exception is made if you wanted to have someone new who never came. One would only recite "Asher bara" as stated there in Ketubot.
This is referenced in numerous sources with no exception stated for a case where for whatever reason one does not have panim chadashot. These sources include Seder Rav Amram Gaon (Seder Eirussin V'nissuin), Rambam's Hilkhot Berakhot (2:10), Tur (EH 62), and the Shulhan Arukh (EH 62:7).
Especially if it's Shabbos or Yom Tov, some have the minhag to say it anyway (Shulchan Aruch Even Ha'ezer 62:8). The "Asher Barah" blessing may be said even if there are no Panim Chadashos (62:7).
Not an authoritative answer at all, but: I have known cases where a sheva b'rachos host would call around to various people to find a last-minute "panim chadashos". As always, CYLOR.