Over the past 4-6 years more and more schools have tried a variety of methods to control the arms-race of scholarship negotiation; one way is asking for people to withdraw from all schools to which they have been admitted and to verify that they have done so when depositing. Here is a link to the LSAC Statement of Good Admissions Practices — a good reference this time of year. Note the strategic ambiguity on multiple deposit policies in the Commitments section.
We could go on and on about the slow evolution of this, but the bottom line is as follows: schools to which you have deposited can run customized reports to see if any admits have paid additional deposits at other schools (only schools where you have deposited can see where else you are deposited — schools where you are WL'd cannot see this information, for example). The report contains names of the deposited applicant as well as the other school(s) to which they have deposited. Most schools likely won’t take full stock of their reports until mid-May, which is when most schools participate in the data sharing (though note that not all schools participate in this information sharing). The operative question you are asking of course is: will a school rescind my offer or merit award if I am double deposited?
In respect to an admissions offer, we highly doubt it. We have never seen this happen. And it wouldn't be the first step anyway — the school would likely contact you first. To rescind someone’s offer is not the easiest thing in the world, and the person whose offer were to be rescinded for this reason could easily take up their case with the school’s GC, the media (an Above The Law article could be overwhelmingly negative and deleterious to a law school that did this, etc. etc.), so on a risk/reward scale it would make very little sense to us for a school to rescind an offer to an already admitted student for this reason. That said, if you are double (or even triple) deposited, don't be surprised if a law school admissions dean contacts you. It can make for an awkward conversation, potentially with the dean asking you to withdraw immediately from the other schools or be withdrawn from theirs. While that may not happen, at the very least you should be prepared to discuss why you're undecided and be prepared to make a decision. Double or multiple depositing buys you more time, but ultimately you will have to make a decision, of course. We've also never heard of a law student attending two law schools at one time (although we do know cases of students planning on this!).
What about pulling a merit scholarship? While, again, I have yet to see it happen for the explicit reason of “we see you have double-deposited, boom, there goes your award,” the risk/reward equation is more balanced for the school here, i.e. it would get money back that it could redistribute or keep because it is way over committed. Keep in mind, however, that when a school looks at its commitment overlap report, it can’t be certain if you have indeed recently withdrawn from the other school where they are seeing you have double deposited. For example, you are deposited at Princeton Law and Dartmouth Law School — Dartmouth sees this but has no real way of knowing if you just called Princeton and withdrew that day. Dartmouth’s information is not entirely precise to the minute/hour/day, and it knows this, so it would strike us as very rash for it to pull your award without first reaching out to you. Plus all of the risk aversion about bad media coverage likely still exists; do you really want to be known as the law school that told someone they were magically less qualified because they simply wanted to have some choice in where they go to law school? Finally, even among law schools there has been some intense debate on the ethical nature of this kind of action. So a school would have to consider its reputation among peers (peers vote in USNWR rankings!) before actually making good on this action.
The bottom line: there are no guarantees, but history and logical reasoning would both dictate that it would be unlikely that you would have anything rescinded before the school were to reach out to you. You too should be risk averse, and one way to be so is to always communicate openly with schools. One final note is that this particular admissions policy is fast evolving; we will try our best to provide updates as we get them.