There's this feature called 'oust' in party management. This has always been a problem in MMOs, even in FFXI where you had to know what you were doing. These people would normally get a /tell or two and then kicked out if nothing happened. If they had a genuine excuse they may be let back in. So just kick these leechers out imo.

If this is your LS doing this and you find it distasteful, find another LS. It's not worth the frustration.