Do a search on 'aircraft, radio failure after departure'. Oz version (typical) below -
1.8 TOTAL RADIO COMMUNICATION FAILURE PROCEDURES
1.8.1 If total radio communication failure occurs in VMC during daylight hours, the pilot shall continue to fly in VMC and land at the most suitable aerodrome. If it occurs in VMC during the hours of darkness (between sunset and sunrise) action shall be taken in accordance with para 1.8.2 below.
1.8.2 If total radio communication failure occurs in IMC, ATC action is based on the assumption that the aircraft will continue to its destination and if unable to land, will proceed to its nominated alternate. Separation standards will be increased and airspace reserved accordingly. (see Appendices ‘A’ and
‘B’ , pages ENR 1.6-9 and 1.6-11).
1.8.3 In IMC, or if unable to maintain VFR, the pilot shall either leave or avoid controlled airspace and areas of dense traffic and establish VFR operation or, alternatively, shall:
a) Proceed according to the current flight plan, at the last assigned flight level, to the clearance limit and thereafter at the flight plan level.
b) Arrive at the destination as close as possible to ETA.
c) Commence descent as close as possible to EAT (or ETA if no EAT has been acknowledged).
Note:
1) Aircraft are to follow the established radio failure procedures as laid down by the respective airports.
2) During this 30 minute period ATC will reserve the airspace at the aircraft’s flight level and below. At the expiry of this period with the concurrence of other users normal operations will resume.
1.8.4 In all cases, the pilot shall contact ATC as soon as possible after landing.