It means 1gh has the ability to do a double spend and 51% attack on Maxcoin(i.e they can spend double more maxcoin than they have, and fork the maxcoin network to nothingness). This coin has no future.
The temporary exodus means that miners are fickle creatures and can and will hop pools as soon as they smell something being off.. but then flock right back again to the pool that has served them best (be that actually the case, or psychological).
Just to address 1gh's > 50%, though.. they have that on many (all?) coins they offer pools for. It's actually in their best interest not to abuse that power on any single coin, as they stand to lose more than they stand to gain. It would be an unwise proposition at best. While I understand people's concerns about any one actor having more than half the network hashing power behind it, those concerns are often misguided. ( don't make me a liar, 1gh )
this just meant, while gh's server was down, miners were automatically switched to failover servers on the other pools, and switched back when it was up again, nothing about service or sth else