In the long run the tracks will start closing if rebates negatively affect their handles substantially.
It seems to me that the tracks should take action now (if legally able) and raise their cut of the takeout of offtrack handle for everyone except other tracks. Accordingly, more money will be available for purses (the horse owners and trainers will make sure of this) and upkeep of the track facilities, etc and the demise of racing as we know would be averted.
Incidentally, I think TVG is one of the only nontrack-based "otbs" to agree to a very favorable takeout agreement for the certain tracks (in return for exclusive rights to their "otb" signals).