As a matter of principle I do not believe in “end of science” as general and end of physics specifically. I really can imagine accelerators in the space, very long, properly shielded and powered with new small fusion reactor or some other source of energy. I do not know if it can happen within next 10 or 100 years but we as humans are pretty inventive and stubborn 😉

It could eg. explain missing mass in our Universe

“what do you think are the limitations of particle accelerators/colliders in achieving even higher particle energies” mainly the issue is the power of the magnetic field that keeps particles in curvature. As far as I know at the moment the biggest “jump” in technology was to switch to magnets operating as superconductors. Since there is no great way to improve that part of hardware the only way to have higher energy which means higher speed (closer to ‘c’) is to make the whole accelerator bigger.