Since the RingCT hard fork, there's quite a backlog of transactions in the memory pool, even a single transaction sitting there for 40 hours already.
Are unmined transactions "returned to sender" after a while? If so, after how long? If not, are those moneroj at risk if those transactions would stay there forever?
Transactions drop from the txpool:
after 7 days if they were included in a block that was orphaned
after 24 hours otherwise
The orphaned block case can happen with invalid transactions, if they were mined by a daemon which does not obey consensus (maybe an old one). This is something that may need a bit more work to determine when to apply the first limit, and when to apply the second one.
Once transactions drop off the txpool, the wallet should notice this in short order, and consider the transaction as failed, and its inputs spendable again.
