  Since 1960's, particle colliders have been in the forefront of particle
physics, 29 total have been built and operated, 7 are in operation now. At
present the near term US, European and international strategies of the particle
physics community are centered on full exploitation of the physics potential of
the Large Hadron Collider (LHC) through its high-luminosity upgrade (HL-LHC).
The future of the world-wide HEP community critically depends on the
feasibility of possible post-LHC colliders. The concept of the feasibility is
complex and includes at least three factors: feasibility of energy, feasibility
of luminosity and feasibility of cost. Here we overview all current options for
post-LHC colliders from such perspective (ILC, CLIC, Muon Collider, plasma
colliders, CEPC, FCC, HE-LHC) and discuss major challenges and accelerator R&D
required to demonstrate feasibility of an energy frontier accelerator facility
following the LHC. We conclude by taking a look into ultimate energy reach
accelerators based on plasmas and crystals, and discussion on the perspectives
for the far future of the accelerator-based particle physics. This paper
largely follows previous study and the presentation given at the ICHEP'2016
conference in Chicago.
