What if some transaction is mined into "orphaned block" ？Some node will remove it from mempool because it is in block. But as it is "orphaned block", the transaction is invalidate.
As you said: "
in a block", orphaned blocks wont be saved in the nodes' blockchain
so, any transaction that's in it that doesn't belong to the valid block won't be removed from their mempool.
is it possible transaction is lost in bitcoin network?
Based from the scenario above, no.
But for other circumstances like being dropped from (
mostly) all of the node's mempool due to long no-confirmation, yes.