Why would the big holders want to attack one of the chains? Their holdings are in both chains, and they can keep, move and sell them independently. Whatever value each branch of the coin has, attacking one branch will kill its value -- which will hurt the holders more than anyone else -- but is unlikely to raise the value of the other branch by the same amount.
The holders should *pray* for a proposed hard fork will EITHER fail quickly to gather any support, OR quickly achieve majority support and end with a clean non-eventful hard fork. Any fork attempt that does not resolve cleanly in one of these two ways can only harm the value of their holdings.
Didn't you kind of answer your own question? An unresolved fork would be bad for holders, so attacking the minority chain to destroy it would make sense if it's not too expensive.
With the first alternative in the second paragraph I meant "fail to gather any suport BEFORE the change is activated, so that the fork never happens and no one seriously thinks that it will happen".
The first paragraph applies if the fork happens, but is not a clean non-event (i.e., if there is a significant fraction of the hashpower still mining the old chain after the change is activated, in spite of the alerts and grace period).
Sorry for the confusion.