I'm curious as to what happens to transactions in orphaned blocks and what happens when a transaction gets dropped.
Transactions in orphaned blocks
They appear when a soft fork happens. All the transactions in the orphaned branch return to the mempool keeping their transaction ID and might eventually be included in some block.
A transaction can be dropped if it spends to much time in the mempool without being accepted by any miner (as was the case with some transactions a while ago when the Cryptokittes app congested the network and raised gas price). In that case the transaction needs to be resubmitted and is granted a new transaction ID
Could you comment on my bold statements and correct them if they are wrong? Also, what is the criteria to drop a transaction from the mempool?