I think they have no idea how to end so they just have to keep going indefinitely at this point.
Seriously though, the talk about it going on for decades is pure delusion. Even with strong ratings what show has talked about going on for years like that? Like it was mentioned Grey's is thinking of ending. Big Bang Theory and Game of Thrones are ending. Soaps are known for going decades and decades and I'm sure their ptb are not arrogant and egotistical enough to think their shows will still be around by then.