Media was told he was available in case of an emergency. When Pyron went out against Miami and Sims didn't come in the media asked Key why. Key responded he was deemed cleared to play in an emergency but not available to play at the time Pyron got hurt. He then said he would leave it at that. Fans ran wild with the idea he refused to play from there.
But being medically cleared isn't the same as being ready to play and foot issues are tricky. It came out shortly after that after consulting doctors the best path for Sims was to focus on rehab.
That was also the last game that he was with the team. If I remember correctly, after that game he no longer attended any team functions. Then he entered the portal to transfer out. Nobody who actually has direct knowledge has said that he could enter but wouldn't, and nobody with direct knowledge has said that he was definitely medically unavailable. The HC's statements after the game were not supportive of an injured player. From what I have seen of him, I imagine that Key would go absolutely out of his way to support and take the heat for any player who is doing his best.
I base my conclusions on the way the HC addressed the situation, and what the player did with and for the team after the incident.
EDIT: Here is a quote from back then:
"In regards to Jeff, Jeff won't be with the football team, really kind of indefinitely now. We had meetings with Jeff and meetings with the doctors and the medical professionals and came to the determination that it would be best for Jeff to not be in meetings or not be in practice, but to be in treatment and in rehab right now moving forward."
Your take on this statement is that he was in rehab. Which is important. However, why would being in rehab prevent him from attending practice to support the team? Whey would being in rehab stop him from attending meetings? If I remember correctly, there were reports that he was not only not attending meetings nor practice, but that he was no longer involved in any activities with the team. To me that sounds more like someone who has already checked out.
My take could be wrong, but there is nobody who has any actual information who is posting on forums. It is all speculation from the same limited information.