Thanks for the responses.
Our make up is
2 Assassin Tank
1 Sorc Dps
1 Sorc Healer
1 Operative Healer
We have tried many of the options suggested. Using predation, LoS even using the snipers sheid. Where it always seems that 1 or two people die.
I suppose its just trial and error untill we find something were comfortable with.
So he casts this at 60% I believe, so at around 63% the sorc healer can bubble everyone, the Sorc DPS can do his own also.
at 61% Marauder pops Transendence (or Marauder version of it) and the Sniper being ~30metres out pops Hunker Down and the Scrambling field.
The SECOND he pops GotM every body should be running out - you have half a raid with force speed the other 3 (Sniper will be uneffected due to hunker down) will be boosted by transendance and their CD - Mara can pop his damage reduction and Merc his shield.
You could even have the Sorc lay down an AoE on the sniper ~61/62% ready for people to arrive.
It relies on everyone being ready to run - even on NiM we don't lose a single person and most >40/50% HP