I personally oscillating between "if the author does not care, why should I?" and "preserve the history". If you are in the second camp, let me remind about my FixingParticipantLinks script which relinks missing bots to strange automata archive.
What is our problem with Java 8? Do we already have bots with Java 9? Or robocode itself is not backward compatible and you see it on big enough robot pull?
My opinion is that as long as a bot works fine on current settings (robocode 188.8.131.52 and Java 8), we should "preserve the history". But once it produces random result (e.g. crashing half of the time), we should remove it (until the author should fix it).
Bots known to crash on some machines:
apc.Caan 1.0 dam.MogBot 2.9 sgp.JollyNinja 3.53