Not happening. Again if india had attacked backed by soviet,it again would have been soviet occupying pakistan and taking over afghaistan, which again usa didnt want 2 see happening.USA would not have asked for Indian bases. The sole purpose of India from day one was to disintegrate Pakistan, they would have urged India to wage a war against Pakistan and given guarantee that USA wont interfere. So an Indian attack backed by Soviets would have meant Pakistan would have been wiped off. Then with clear ground they could have used any means to get weapons to mujahideens. Even if this was not possible they would have bombed Pakistan to get weapons in Afghanistan. Post 9/11 Pakistan gave a hint that they wont support USA in Afghanistan so in return George Bush said we would bomb Pakistan back to stone age and then attack Afghanistan through Pakistan.
Secondly, china wudnt have sit silent if india had attacked. Cuz if u rem in 65 war , soviet and usa both had rush for the ceasefire, one fear was china jumping into it.(what i have read)