My understanding of the CBA states that you either lose or can't use a TE when you are under the cap.
However, I believe until July 1, we are not "under the cap". If we don't use our TE tomorrow, we probably won't use it.
We could trade Sergio to New York for their TE. Two years ago, the only way we got the 24th pick, that landed us Rudy, was by using our TE to also take on James Jones' contract (in two separate deals)that Phoenix didn't want to pay; something like that could happen, but is unlikely given our goal to increase cap space.