No pilot will ever get into hot water for complying with an RA. ATC may be asked what (if anything) they could have done to prevent the RA happening in the first place.
The comms failure procedures depend on the flight being either VMC or IMC. If IMC, then follow the procedures to destination.
That is why many other countries require flights departing from VFR aerodromes to remain VFR until the IFR clearance is received. If they get a comms failure before they get the clearance then the VMC procedure applies.
Unfortunately, in the UK many VFR aerodromes such as Fairoaks are designated as IFR aerodromes and flights can depart IFR in IMC. Quite ironic that a place like Fairoaks can have IFR arrivals but can not have instrument approach procedures unless there is ATC. They can however have aircraft departing IFR into IMC at 50ft, 30 seconds apart with the faster one behind. Safe?
Even MATS1 makes it clear what is going to happen when the IFR flight you are talking to has a comms failure;
Receipt of flight plan data does not constitute a clearance, except that when ATC has acknowledged receipt of the information from an aircraft in flight and radio failure occurs before a clearance can be transmitted, the aircraft may be expected to proceed in accordance with the flight plan. Aircraft should be given a clearance in reply to an in-flight request, but if this is not possible the aircraft are to be advised to remain outside controlled airspace, when to expect clearance and given a time check.
If you read the above, you will also see that you do not give a clearance to aircraft to remain outside controlled airspace - you "advise" them to do so.
The situation is not ideal by a long way for both ATC and the operators. We have requsted more appropriate airspace and procedures. Not nice but I think that there will eventually be a "we told you so" situation and then things might change.
Regards,
DFC