The only way Chabad would be ‘vindicated’, so to speak, is if Moshiach turns out to be the Lubavitcher Rebbe.
Not at all. Chabad will be vindicated when Moshiach comes, regardless of who it is. It will be more vindicated when the Rebbe returns to “lead us to meet Moshiach”, as he often put it. And of course if he does turn out to be Moshiach after all it will certainly be vindicated, but that’s completely unnecessary.
Moshiach’s identity is completely unimportant to Chabad. Of course during the Rebbe’s life most of his chassidim thought he would be the one. It seemed completely logical. But even then, had Moshiach come and it was someone else everyone would have been delighted. After his passing the probability of his being Moshiach is obviously lower, but so long as some chance remains most of his chassidim still hold out hope for it. But obviously if it’s someone else they will be just as happy, and will wait for him to return and confirm for them that this person is the real moshiach.
(To quote at least one Gadol, let it be the Lubavitcher Rebbe, as long as he comes already…)
And any Lubavitcher would say let it not be the Rebbe, so long as he comes already.