In my honest opinion, slim to none. From what I've heard, Abarai-san was actually very careful. He was the only one who infiltrated Las Noches, and was wearing my reiatsu concealers at the time...I'd say that from the number of them he ordered from me he used only my kidouless kidou to destroy the lab, so there should have been no trace of his presence therein.

I'm inclined to believe that if Aizen brought the Octava back it was because he needed him...indicating to me that he can't make full sense of Szayel's research without him...meaning that even if Szayel had some sort of tracking mechanism on him that would record something in the event of his death, it's likely Aizen wouldn't be able to access it anyway. Especially with the lab now destroyed.

So I would say that his having actual proof of exactly who is to blame for what happened is probably impossible.

But I'm not sure how well that pans out for the rest of Soul Society.