Depending on what happens in Avengers 4, there's a likelihood that Scott will still be running around as Ant-Man, fighting crime on the streets of San Francisco. So not only would this explain his absence for most of X-Con: The Series' day-to-day operations, it would also leave things open for him to pop in from time to time. Thinking about how Maggie and Jim will probably still be caring for Cassie, depending on what timeframe we're looking at post Avengers 4, and remembering that Scott is still a vital part of X-Con's operations, he kind of has to be there. It doesn't mean that Paul Rudd has to commit to a long term role in the series, though if by some miracle they could land Rudd's talents on a more regular basis, that would be icing on the cake, and a fun way to keep the Ant-Man franchise developing in the background.