it doesn't matter, Aizen has no interest in attacking Soul Society until after he gets the King's Key. And it doesn't take that long to travel from Human World to Soul Society.
Ikkaku is there. I suppose he can hold off 1 espada at least.
Captain Yamamoto has always displayed a strange way to deal with crisis, i.e. deploying people to the wrong place for the wrong cause, but eventually, he manages to get things done right.
3 Defectors
4 Trap at HM
6 Waiting for Aizen to show up
Factors that may tip to SS side:
8 vaizards support SS
Urahara / Yoruichi and team
Ishinn / Ishida Dad
The Vice Captain hold the defence on SS
Factors that may tip Aizen to win:
8 Vaizards support Aizen cause
Vastrolord can handle 2 Captain at a go
Aizen in super bankai mode
Ichigo team and the 4 captain remain trap at HM without interrupt any fights
Aizen already assemble the remaining vastrolorde to replace the fallen espada.