what are my chances of gifting alien invander heim?

My friend loooooves heimerdinger and really wants alien invander (its a legacy). I really want to try to myserty gift it to him since I have single handled myserty gifted him: SG udyr, high noon yasou, underworld TF, and K9 nasus.....should I try to do the mysery gift or will it come out of the vault soon? I was saving for arcade riven, but I just dont want it anymore. He gave me steel legion Garen and I just want to be a good bro.