This might be a wrong question(I am new to understanding bitcoin details). But I want to ask this: What happens if one node finds nonce value that results in way more leading zeros than expected by the target?
Nothing special happens in this case.
If you find a nonce for which the hash has at least the necessary number of zeros (or more precisely, is numerically less than the target value), you have a valid block. That's all. As far as I know, the Bitcoin protocol pays no attention to whether there are "extra" zeros.
Of course, if someone submits a block header with a drastically large number of extra zeros, people might reasonably take this as evidence that they have broken the SHA256 hash function in some way, perhaps with some sort of preimage attack. This might lead to developers wanting to phase out the use of SHA256. But that's beyond the scope of the protocol or the software.