It depends. I think you can rebuild with Crosby. The contracts currently are staggered on the team. Crosby's ends on 2025, Malkin 2026, Letang 2027, Karlsson 2028.
I can't say this with any definitiveness but Crosby seems like one of those workaholic types that could adjust his game and play until his mid-40s. If he retires at age 43 that's 2030. Malkin and Letang will definitely not make it that long. Karlsson will likely be traded before his deal ends. I foresee us being mid-to-bad for the next three seasons. Malkin retires after 2026. Letang gets sent to Robidas Island for something. Karlsson is traded at 50% retention that summer and in 26-27 and 27-28 the Pens are Horror-bad.
Would a 43 year old Crosby mentoring a young up-and-coming 29-30 Pens squad be out of the question?