Sean Carroll has some good talks on this. Basically there's two frontiers: intensity and sensitivity.
With intensity going past LHC is looking very difficult but not necessarily impossible. There's been advances in compact linear accelerators that look promising.
With sensitivity we're got a lot of untapped potential to observe high energy particles/physics produced by nature.
I don't mean to trivialize the difficulties but there's reasons to be optimistic about us learning new physics in the coming decades.
With intensity going past LHC is looking very difficult but not necessarily impossible. There's been advances in compact linear accelerators that look promising.
With sensitivity we're got a lot of untapped potential to observe high energy particles/physics produced by nature.
I don't mean to trivialize the difficulties but there's reasons to be optimistic about us learning new physics in the coming decades.