Heaslip like Zebo is a definite in the squad when fit, but definitely not indispensable with the raft of backrow talent coming through. Even fit he'd have a dogfight on his hands to start for Leinster these days. I don't think many people view Heaslip in as high a regard as Alpha, but letting your captain leave the country isn't a good look for the IRFU either. He shouldn't and won't get another one I'd say, and I don't know how much he's on, but a CC at the least is understandable.
These long central contracts do seem to be shortsighted in the cases of Bowe and Robnoxious (honestly you wouldn't give Healy one on this form, but hindsight and all that), but the nature of central contracts is they offer security to guys on the fence worried about injury destroying their earning potential. That means a relatively long contract to make passing up on France worth it.