I tend to think that not only most would stay, but even if shunning as a rule was dropped, most 'faithful' witnesses would still shun those who leave, since shunning would now be "a matter of conscience" (you can't force them to talk to you anyways). The only quantitive (and not qualitive) difference would be that more witnesses would talk to their DF'ed friends, but hardly to apostates. The conscience of most non-awake jws would still compel them to shun apostates at least.
On the other hand, I think there's this delicate balance between the cultish/totalitarian and religious aspect of WTS: the cultish/totalitarian part is prone to collapsing if inserted freedoms, as happened in the Soviet Union. The religious part is immune to collapsing, since many(most?) jws shun or pray or whatever, not because they're forced to, but because their faith (false but faith nonetheless) is so deeply rooted in their hearts and minds that they actually want to do it.