The odd thing is it should only delete wallet.dat if it doesn't see a file called wallet.dat where it expects to. It should attempt and complain about a wallet.dat that it cannot read or understand it's structure. You could check read/write/modify in file properties. I take it as read that you already checked the log file (in the same directory or through the LTC gui in 'console'. This should tell you step by step what the node does when you drop your .dat file in the directory and fire up the LTC node.
Maybe you should try an older build - see if that can read your wallet. Even if it can't sync and shows an empty balance it will still incrementally update the wallet.dat file itself whils leaving your private keys intact.

Meanwhile you could also start the same thread in the Bitcoin section and substitute Bitcoin client for Litecoin client in your question as it is very likely that the issue you are having could just as easily (and possibly more likely) be answered there.