What are the odds? Pretty good I would say.
121.5 is monitored by all the overflying airline stuff and by marine vessels, too.
Even if you don't get DIRECT contact with ATC on 121.5 (but the position in mind did get Dublin on VHF) then you can almost certainly get a relay to some ATC unit through some other operator.
Even if Valley did suggest they didn't work at weekends - they will still monitor 121.5 (and they are the ones with the helibeaters sitting on the ramp just waiting for that very instance). Who better to talk to?