ENR 1.1-2 3.7. An air traffic clearance proposed by ATC DOES NOT relieve the pilot from complying with satutory requirements NOR from the responsibility for the ultimate safety of the aircraft.
IMHO if not getting a clearance from ATC was such a crtical matter for flight safety worthy of suing ASA (disregarding the time already spent out of gliding range) then THE PILOT IN COMMAND is the one responsible. If the clearance was not available then the word require or a phrase declaring an emergency should have been used. It is the pilot in command in this case who should sue himself (IMHO).