With regards to people leaving warzones, with the slightest hint of loosing i have the following recommendations (apologies if this has already been suggested):
a) 'Time out'
The chosen pvp player gets locked out for 30 min and cannot join any warzones. The activity is monitored over a week. Repeated violation will end up player getting 2hr ban, then 24 hr and eventually 'no commendations or valor' or being disqualified from being mvp (either at the end or all along)
b) 'Wrath of the Empire' buff - 'Retribution of the Republic'.
The suggested names may change but essentially the team loosing a player gets a buff, stat boost. this can be in form of a shield enhancement, or something similar to lower levels joining warzones. Once again boost is incremental on the people leaving.
*imagine God mode, if everyone leaves on the team except you:D*
Kindly replay back if you like option 'a' , 'b' or have and another suggestion here