I think losing contact for an hour is unusual, but not being in contact with ATC for a few minutes is pretty common. As you fly ATC will hand On a cross the US flight you offmight hear 5-6 incidents. Most of these seem to occur as planes are handed off from different sectors that use different frequencies it. It not uncommon for the pilot to tune in the incorrect frequency.
Also, as aircraft descend into fields with obstacles (ex. mountains) it is not unusual to lose contact. As you fly along you sometime herehear ATC attempting to contact a plane and get no reply. If you have just heard that call sign you might volunteer to give the aircraft a call and then act as a relay. For example, you are over some place and hear ATC: "KingAir 123 contact center on 123.55" KA123: no response. ATC: "KingAir 123 contact center on 123.55" KA123: no response. ATC: "KingAir 123 over someplace contact center on 123.55" You: "Center, N12345, we are over someplace, would like us to try to contact KA 123?" ATC Center: "N12345, affirmative, contact KingAir 123 and ask them contact center on 123.55" You: "KingAir 123, N12345, center would like you to contact them on 123.55" KA123: "Contact Center 123.55, thanks N12345"