Definitely a dark story but it does address an interesting point. If conditions had become that intolerable at the Dursleys', would the protections have failed? I can imagine Dumbledore's shock if/when that happened and his profound and sincere regrets afterwards, but it might be way too late then. He risked quite a lot on a very chancy ward.
Given the way the Dursleys act, I can see the Bond failing a couple of ways. The Dursleys have to 'accept' Harry, but as we saw in book six, they did so under duress only. What if that had not been enough?
All in all, the Charm's protection was not worth the pain, in my opinion. (Especially after what we find out in the end of book seven.)