He did seem subdued. And his remarks were about how encouraged he is by the appointments President-elect Trump has made so far. Romney said that gives him hope, which indicates to me at least that he still has doubts. If so, he's not going to be in the cabinet.
Worth remembering that GHW Bush trashed Ronald Reagan for their entire nomination campaign.
Reagan asked him to be Vice Prez. Well beyond SoS. Bush said yes and served well.