I think it is too early to say because all three coasters appear to be in good form, ask this question again in five years time.
Really you either have to build a new rides that fits the trenches and tunnels or you have to spend a few hundred thousand relandscaping the placeI foresee retracking or an overhaul of Nemesis, but I don't think that meets the criteria for "going".
Probably Oblivion, but it's quite a small footprint and I wonder what you could put in its place.
If they remove Nemesis then the park would have the challenge of beating it which would be very difficult and expensive.You say that but it may be that they require the area for new attractions? Maintenance costs my sore who knows
Surely there's already a topic for this somewhere? I feel like it gets asked at least once a season.