Can the forum provide an option to the OP of posting the last post before the Post will be locked? For example OP getting the PM by Forum saying something like "Your Post [PostName] will be locked in 24 hours so write if you've anything to say"
Moderators do not just lock a thread, it is done in a way nobody will be able to complain about the locked thread, there are many threads that are later full of low quality posts but not locked by the moderators, only few are locked, and if you have any good reason for the moderator to open the thread, you can create a thread about the good reason on meta board, if the reason is seen reasonable, I think it would be unlocked for you, but I am still wondering how such a long thread will be unlocked. As suggested by hugeblack, if you do not want your thread to be locked this way, you can create a self-moderated thread.