There's also brief glimpses of Megaroad 1 in the first episodes of both Macross 7 and Frontier.
Timelines say it was in contact with Earth for four more years and then suddenly, all contact was lost. The Macross Government covered that loss of contact up for a further twenty before finally admitting they had no idea what had happened to Megaroad 1.
And in a sense, I don't want to see more. Hikaru, Misa and Minmay flying off together is a perfect way to bookend the series and gives them a sort of immortality. Hell, they could have folded back in time somehow and *become* the Protoculture for all I care, I'd just rather it be left a mystery for all time. Some things should be.