transaction stays in status "0/unconfirmed, in memory pool" to say this upfront: I know these kind of questions have been asked before, but I already tried some things and I really don't have the knowledge what to do next. 

I recently tried to send an amount of BTC from a Bitcoin Core wallet. After one whole day, the transaction still has the status "0/unconfirmed, in memory pool" in Bitcoin Core.
I've tried restarting with options (rescan; zapwallettxes), but it didn't work. I also used the dumpprivkey command and imported this key into a blockchain.info wallet. It says there's no money on it...

How can I get this money back?



Edit: Solved. Like Michael C Ippolito said, the transaction has been confirmed eventually. I thank you for your answers.
One cannot say for sure what is happening without seeing the transaction ID, but it's likely that this is being caused by the current transaction backlog of about 62,000 or so unconfirmed transactions.

If the transaction being discussed has a low fee (relative to the other 62,000 unconfirmed transactions) the transaction being discussed may not be confirmed until a large number of those other unconfirmed transactions have been confirmed.

Two possible outcomes are that the transaction is eventually confirmed or that the transaction will eventually get dropped from the network and you will still have control of those bitcoins.

EDIT: BIP 125 Opt-in Full Replace-by-Fee Signaling provides a flagging option for dealing with this, though I'm not sure if any Bitcoin clients currently provide userfriendly support for this.