My normal on-death rule is that the new PC starts with half the XP of the old PC. This worked fine in 1e-2e where it normally just meant the new PC was a level behind. For 3e I'm willing to decree a minimum starting level though, which for a large PC group will be the lowest level of the remaining PCs. Generally I want to avoid too large a disparity in levels amongst the PCs, since it tends to be self-reinforcing - lower level PCs are weak, weak PCs die more. Currently group is 9th-12th level, and if PCs die, new PCs come in at a minimum 9th level.