AFAIK Muse is not a group cast spell and is single cast. When it comes to Bard group spells they tend to be the cyclics and the ones that are not are cast upon the Bard then go to the group. As long as they cast the spell on you then it shouldn't matter if they stay or not.

> The only ones that end their effects if either you or the bard leaves are their cyclics and the ones listed as pulse to group on the Bard spell page in the skill column. All other spells are as you are used to.

For a quick reference, whisper's of the muse is really the only bard spell that can straight cast onto someone else. Nexus (and tongues?) continue to work when the bard leaves, but you're tied to the area the spell was cast in. Everything else will go with the bard when they leave.