You haven't pointed out any problems with Bitcoin or Bitcoin Core. When you "send" bitcoin to another address, until the transaction has been secured in a block, it is not final no matter what wallet you are using. It is a really bad idea to delete you wallet until the transaction has gone thru, and given how small the wallet file is, it could be preserved indefinitely just in case. What if someone (or yourself) who had sent coins to that wallet in the past accidentally reused an address? That bitcoin would be permanently lost if you did not keep a backup of your wallet/keys.