Historically, it actually seems that the Serbians were prepared to capitulate to the Austrian demands this is evidenced by Pasic's telegram on July 25th where Pasic said Serbia would be "conciliatory on all points" and give Austria "full satisfaction. This view was confirmed by a telegram sent from Crackenthorpe to Grey that same day. It was only the Russian reply that completely changed the stance of the Serbian government.
Nah...Serbia was firmly opposed to points #5-#6 of the Austrian ultimatum. In fact, the Russian response (which was...discouraging, to say the least) made Serbia slightly more willing to consider full acceptance of the ultimatum.
See Decisions for War by Hinley and Wilson - Chapter 3.
As for the main question: if Russia refuses any support - as in, doesn't even maintain some diplomatic pressure on Austria - then the exact text of the Serbian reply probably doesn't matter. Even if the controversial point is nominally accepted, Austria will likely declare the response unsatisfactory due to some technicality and attack Serbia anyway - this, after all, was its actual goal to begin with. What follows is a military, political and humanitarian debacle for Austria - but one that Austria can't exactly lose.
Expect WWI to break out in a year or two, due to continued tensions between the Entente and the emboldened and increasingly aggressive Central Powers.