How would you handle the same situation but, the intermingled cards did not contain an indication that the all-in were beaten?
You mean if, using the above example's 259TA board, the four mingled cards were something like 78TT, with the all-in having an Ace?
I.E. Each blind could have had a pair of tens and lose to the all-in's Ace, or one of them could have had trip tens eliminating the all-in. And no surveillance?
Hmmm... Tough situation. And makes me re-think my initial response above.
TDA Rule 13A says "Proper tabling is..." The first word is 'Proper'. If the cards get intermingled, they weren't properly tabled.
Of course, one of the blind could say he tabled his hand, but the other blind threw his cards in causing the intermingling. That leads us to 13B.
TDA Rule 13B says "At showdown a player must protect his hand while waiting for it to be read". Clearly, neither blind protected his hand.
So, with those two rules, I'd rule both blind hands dead. And that goes for the original situation where you know one of the blinds would have knocked out the all-in, but don't know which.
What if the four cards were able to be identified and/or the blinds had no argument about whose cards were whose? I'd allow their claims to stand, unless any player objects. At that point, I's still kill the hands and invoke Rule 1.
And that leads me to a NEW question: If as I suggest, there was no argument, would the dealer be obligated to call the floor?