I would say that if your primary concern is social skills, individual therapy in isolation is unlikely to offer him a great deal more at this time, as what he needs is transfer training. Having the social cognition in isolation is not going to be that much of a challenge for a high-cognitive child. It's all the subtleties and permutations in a live situation with another child that create the challenge.
IOW, he needs practice. I think conversations with his current and next-year's teacher may be in order, to establish what his baseline is in kindergarten, as far as how he interacts with peers, and to allow the sending and receiving teachers to share insights into where he is strongest, and where he benefits from adult coaching. It may be helpful to sit down with the school psych and/or adjustment counselor/social worker, and have this same conversation. He or she is in a good position to provide consultation to the classroom teacher on cueing and coaching in the naturalistic setting, and may even be able to go in to the classroom ever so frequently, or set up a friendship group at school.
I would also talk to his current therapist about what she thinks should be his next set of therapeutic goals, and what criteria she would use to measure progress toward them. This way, whether you continue with therapy right now or not, you will have some idea of what to watch out for.
