[Tompost]

can they leave and i kill it solo?

dunno about that specific boss (far away for me ;)), but if they leave, and noone clicks the "fill group" thingy, you're alone in there. Just check on the right side at duty finder (this *is* a duty finder instance, no?) if it says "searching for members". If it doesn't, all is good. Otherwise you have the risk that someone enters while you're wildly porting through the air, taking risk of ban report.

......... Coil is not in DF = =